it occurs when you feed items to your pet(in my case: pink dandelion ). After that pet just eat every drop you get from battles. (i said they eat it, because after battle instead of hearing the gold sound, you hear the sound when you feed something to your pet.) Only thing you receive is exp.
Fix : Only way i can fix it close and reopen wizard101. (unequipped pets will not work)
This usually happens after you feed an item to your pet and get xp. You do get the drops they just don't show in window. The best work around for this is to simply feed your pet another item. If you get tc, reagents, or just gold the drops will show as normal.
I actually thought they fixed this little bug. It must have came back.
i've tried what Hkboy7 said, and i guess entering an area without closing feeding windows does cause it. (EDIT) turns out i DO receive the drops, it just doesn't show up on the left or in chat box. (+ annoying sound).