Using a vial on a cup stealthily (pickpocketing)  in inventory removes both items from inventory until relog, and does not show any message.

1. Click vial with pickpocketing
2. Use on cup
3. Both disappear
4. Return on relog

Doing the same but to a cup on the floor has its own oddities

1. Vial is not used
2. Only worked some of the time. Could be a timer? But it seemed random on my end