I've been playing vanilla Minecraft and everything was completely normal. I then decided to add a few mods such as Optifine, Forge, Biomes O' Plenty, and Mutant Creatures (Incase this is important, the order I downloaded them was first Optifine, then Forge, then Biomes, then Mutant, just as I listed them before). After I successfully downloaded all of those mods, I then began to notice, while I was in Creative Mode, that I was "missing some items." When I scrolled my mouse over them (in the Creative Mode hotbar thing), however, the name of the items appeared which means that the item was actually there, but was invisible. I tested it on Survival, too, and witnessed the same results (killed a cow and the lether and raw beef WERE in my hotbar, but weren't visible). Do you guys know any ways to fix this problem? Thanks.
P.S.: Also in case this is important, or needed, the version of Minecraft I am using is 1.5.1.