Quote fromQuote fromits a known bug. trees that existed before the update pretty much got their leaves randomized for reasons that nobody understands.
No the reason trees have random leaf blocks is because before the update Minecraft assigned random values for each block. Easy to understand. After the update when those values were used in game the kind of leaf changed to match the new system.
So it's probably not fixable? All trees in any pre-update worlds are permanently broken? That sucks. All that work growing a huge tree for my treehouse is wasted. At least now we have bone meal to make trees a little more quickly.
I guess what I'll probably do is edit my texture pack to make all the leaves the same shape (if not color) -- just replace the pine needles with the default leaf texture -- until I'm ready to start over in a new world.