Update: I've actually noticed that if you start with a smaller stack, it will only let you create as many full stacks as items you had in your original stack. EDIT: just to make it clear, for this, you just take the stack and middle-click-drag it into the inventory
I just want to point out that I've been seeing this in 12w25b
I've also noticed this
I've now tested a 64-stackable item in a 'triple-chest' (shameful I know, using a bug for investigating another bug), and I've noticed that it tries to copy only 64 stacks, and won't go any farther. It looks like my theory is holding so far.
I think I have a theory on why this is the case: Since this functionality is related to the functionality of splitting a stack by left-click (or right-click) dragging, I think that there is a restriction that in the other cases would prevent splitting the stack so far that it can't cover the slots requested. Since a full stack of eggs is 16, it's trying to say it can't split any farther, even though it's not actually splitting the stack (it's copying them.). Basically: this is a carry-over restriction that ought not to apply to this specific feature. I hope what I said makes enough sense to be useful.
It still affects 1.8.2-pre1