Hi Laserrobotics. Two facts rule out server-side shenanigans:
1. mafia invokes HP auto-restore before drinking the next drink, so it knows that a mug is going to be used next.
2. mafia's inventory count of frosty mugs decrements by 1, which it couldn't know if it was server-side misbehaviour.
Completed for confirmation:
0. Had previously put frosty mugs in the closet and unchecked "Take items from closet whenever needed" to stop the problem from occurring.
1. Logged into KoL with browser only (cache clean), took frosty mugs out of closet, drank booze. No frosty mug used. OK.
2. Logged into newly launched mafia, drank booze via inventory, CLI and Item Manager, no frosty mug used. OK.
3. In Item Manager, queued up a frosty mug and booze, drank, frosty mug used as expected. OK.
4. In CLI, drank booze, frosty mug used unexpectedly, no log message about a mug being used, log message about HP loss.
5. Checked "Take items from closet whenever needed", put frosty mugs in closet, drank booze (successfully), got message Consumption helper failed, and a frosty mug and the booze appear in the Item Manager queue, frosty mug was not taken from closet.
6. Exited mafia, re-launched, drank again with frosty mug in inventory, no frosty mug used. OK. (This contradicts my prior assertion that "I always shutdown and restart mafia": I must have been mistaken. bmaher, this corresponds to your statement that the value is in-memory only).
So anyway, somehow after using one frosty mug mafia thinks all future drinking must also use frosty mugs. Can workaround by closing and restarting mafia or by putting frosty mugs in closet and unchecking "Take items from closet whenever needed".
EDIT: Using a frosty mug via the relay browser doesn't seem to trigger the issue. It is specifically related to using or queueing up a frosty mug in the Item Manager.