Diamond Tools/Bow / armor durability bar not showing up (enchanted items)

when playing, I noticed the durability bar didn't show up on the diamond tools as well as on the bows.
the F3+H key still work to show the number, but the bar itself doesn't work.

EDIT: the armor is also affected (all armor types, not just diamond)
doesn't seem to matter wether there is unbreaking or not.
also it seems that only the enchanted items are concerned