Just wondering, were you in 1.8 by any chance? You might as well have thrown your item away by renaming it:
Each time an item is worked on an anvil, even if only a rename, its prior work penalty is multiplied by 2 and 1 level is added. Thus, if an item has been worked N times the penalty will be 2^N - 1. After six workings, the penalty will be 63 levels, making any further repair or enchantment impossible in survival.
(by contrast, prior to 1.8 renaming was the most important thing you could do with an anvil; that said, renaming an item at the same time as repairing or combining doesn't incur any extra charges beyond the cost of a rename, but it isn't really worth the one level when there is no real purpose to it, maybe if you have something that you know will last a long time, such as my "Ender Pickaxe", an Efficiency V, Unbreaking III, Silk Touch I diamond pickaxe used on Ender chests, and still around 80% durability despite never being repaired)
Also, I've used anvils hundreds (the last time I looked, I'd gone through something like 33 anvils, with an average of 25 uses per anvil or over 800 uses) of times and have never had an item simply disappear - though it will be thrown out when you take it out of the anvil and it breaks, which may be what happened in your case.
Yes i am in 1.8..... Mojang better fix that, dang that stinks.....
It is probably because they want you to enchant, which probably also goes along with making lapis useful for something other than decoration and blue dye (which are really the same thing, as there is nothing non-decorative that requires lapis).
To be fair, they did make it much easier to enchant, so not being able to keep using an item forever, as long as you don't lose it, isn't really a problem in most cases, plus the costs don't depend on enchantments or durability; previously, many enchanted diamond items with more than just two enchantments were only repairable with individual diamonds; for example, my Sharpness V, Knockback II, Unbreaking III diamond sword costs 35 levels for two diamonds - this is far more expensive than even the last repair possible in 1.8, which costs 33 levels for a new sword, restoring twice the durability for the same number of diamonds and a bit more XP, despite the increase in XP per level; all other repairs cost far less, more than making up for the costs of enchanting a new one (not that spending 35 levels is an issue since I get over 6 times the XP required back from mobs killed, and with Unbreaking I use less diamonds, and less XP per use, than repairing one without it with a new sword).
Also, an enchanting tip - have multiple items that you want to enchant on hand so if one shows something that you don't want try a different item and see if you get what you want on that one (e.g. sword shows Bane of Arthropods, but chestplate shows Protection; if not that, then your bow might show Infinity, and so on), you can also put a torch in front of a bookshelf to lower the maximum level (e.g. 28 instead of 30) and still get good enchantments. Even if you enchant a junk item for 1 level you only lose about 1/8 the XP that you would before 1.8 (spending all 30 levels), you might even wait until you have 31 or 32 levels before enchanting, which only costs a bit more XP (level 29-30 requires 107 XP, 30-31 112 XP, and 31-32 121 XP, and lets you enchant 1-2 junk items before returning to getting more XP).
It is also worthwhile to use the anvil to put Unbreaking III on any item - but for armor only if you use a fresh Unbreaking III book (i.e. not made by combining lower levels), and even that isn't really worth it IMO (Unbreaking III increases armor durability to 143%; losing one repair leaves you with 83% of repairs left; 143% x 83% = 119%); luckily, Unbreaking III is the most common armor enchantment at level 30 (30% chance on a diamond chestplate, compared to 15-16% for Protection IV).
You can just call me Canary.
How not to look like a total fool in the forum games
(by contrast, prior to 1.8 renaming was the most important thing you could do with an anvil; that said, renaming an item at the same time as repairing or combining doesn't incur any extra charges beyond the cost of a rename, but it isn't really worth the one level when there is no real purpose to it, maybe if you have something that you know will last a long time, such as my "Ender Pickaxe", an Efficiency V, Unbreaking III, Silk Touch I diamond pickaxe used on Ender chests, and still around 80% durability despite never being repaired)
Also, I've used anvils hundreds (the last time I looked, I'd gone through something like 33 anvils, with an average of 25 uses per anvil or over 800 uses) of times and have never had an item simply disappear - though it will be thrown out when you take it out of the anvil and it breaks, which may be what happened in your case.
TheMasterCaver's First World - possibly the most caved-out world in Minecraft history - includes world download.
TheMasterCaver's World - my own version of Minecraft largely based on my views of how the game should have evolved since 1.6.4.
Why do I still play in 1.6.4?
Yes i am in 1.8..... Mojang better fix that, dang that stinks.....
It is probably because they want you to enchant, which probably also goes along with making lapis useful for something other than decoration and blue dye (which are really the same thing, as there is nothing non-decorative that requires lapis).
To be fair, they did make it much easier to enchant, so not being able to keep using an item forever, as long as you don't lose it, isn't really a problem in most cases, plus the costs don't depend on enchantments or durability; previously, many enchanted diamond items with more than just two enchantments were only repairable with individual diamonds; for example, my Sharpness V, Knockback II, Unbreaking III diamond sword costs 35 levels for two diamonds - this is far more expensive than even the last repair possible in 1.8, which costs 33 levels for a new sword, restoring twice the durability for the same number of diamonds and a bit more XP, despite the increase in XP per level; all other repairs cost far less, more than making up for the costs of enchanting a new one (not that spending 35 levels is an issue since I get over 6 times the XP required back from mobs killed, and with Unbreaking I use less diamonds, and less XP per use, than repairing one without it with a new sword).
Also, an enchanting tip - have multiple items that you want to enchant on hand so if one shows something that you don't want try a different item and see if you get what you want on that one (e.g. sword shows Bane of Arthropods, but chestplate shows Protection; if not that, then your bow might show Infinity, and so on), you can also put a torch in front of a bookshelf to lower the maximum level (e.g. 28 instead of 30) and still get good enchantments. Even if you enchant a junk item for 1 level you only lose about 1/8 the XP that you would before 1.8 (spending all 30 levels), you might even wait until you have 31 or 32 levels before enchanting, which only costs a bit more XP (level 29-30 requires 107 XP, 30-31 112 XP, and 31-32 121 XP, and lets you enchant 1-2 junk items before returning to getting more XP).
It is also worthwhile to use the anvil to put Unbreaking III on any item - but for armor only if you use a fresh Unbreaking III book (i.e. not made by combining lower levels), and even that isn't really worth it IMO (Unbreaking III increases armor durability to 143%; losing one repair leaves you with 83% of repairs left; 143% x 83% = 119%); luckily, Unbreaking III is the most common armor enchantment at level 30 (30% chance on a diamond chestplate, compared to 15-16% for Protection IV).
TheMasterCaver's First World - possibly the most caved-out world in Minecraft history - includes world download.
TheMasterCaver's World - my own version of Minecraft largely based on my views of how the game should have evolved since 1.6.4.
Why do I still play in 1.6.4?