This is an odd one
Renamed Interface/WTF and installed nUI fresh with no other addons so I could see if I could replicate the issues....
If you put a macro (any macro) in slot 1 on action bar 1, and the macro has a name, that macro name will appear on each food item in the pet feed window (the number of how many food items appears as well as the picture of the food item, too).
If you free up slot 1 on action bar 1 (make it empty), then each food item in the pet food window is completely blank.
If you drag a spell from the spellbook into slot 1 on action bar 1, you can see the food item in the pet food window, but no numbers appear to tell you how much of each food item you have. /nui rl fixes this.
Last night I had not updated nUI (not the latest emergency release or the one before), and in Naxx the pet food window got stuck on open lol. We're supposed to do Nax again this evening to down Kal (wish us luck!), and if I get the chance I'll see if the window gets stuck again.
No bugsack errors while feeding though
Let me know if you need any other info, and thanks for all you do to keep nUI updated and our nUI addiction fed!