I'm mastering a game using the MERP second edition rules. One of the players was lucky enough to start with an Item which contains a daily spell, which he chose to be Invisibility (from the Illusion path) which is a level 4 spell. As the rulebook states, if the spell chosen is of level 4 it can be used once a day.
4 - INVISIBILITY (E) As Unseen, except everything within 30cm of the target is invisible as long as it starts and remains within the 30cm radius.
Unseen in turn says:
2 - UNSEEN (E) A single object (or being) is made invisible (1 garment, 1 naked body, etc.) until 24 hours pass OR the object is struck by a violent blow (being hit by a weapon, falling, etc.) OR the object (or being) makes an attack.
The spell grants the user invisibility for 24 hours, which is a whole day. The player is trying to abuse the system by not leaving his invisibility state and reactivating it right after 24 hours, not stopping from being invisible ever. He waits for the spell effect to finish before executing his move, in order to become invisible again without spending too much time being visible.
(The other players are fine having an invisible, one-action-a-day companion. As long as he helps with acomplishing their goal, they don't really care about not seeing him. In addition he's sharing his earnings so everyone's happy. Of course he has not been invisible for the whole campaign, just whenever they enter a new location, when he starts his stealing rampage while the rest act as normal people gathering information and so on. He'll leave his perma-invisibility when facing bigger dangers and the rest of the team needs help, but he'll usually wait for entering combat.)
As it's just too powerful because it's not using any of his power points I tried to limit it by making the cooldown of the item start when the effect stops, but the player claims that the item, just as a human caster, does not need to keep casting the spell to become invisible, so the cooldown for the item should start counting since it was cast.
He is right in his statement and I can't disagree with him, so he's free to rob/steal or even kill if waiting for the 24 hours of the spell coming to an end before striking his blow to the objective to then become invisible again.
Is there a rule which restrict this kind of abuse or did he made a really nice strategy to advance through the game?