If a worker forgot a sheave in a field, thereby making it Shich'cha (one of the gifts which the owner of the field must leave to the poor), does he have to pay back the owner?
The mishna in Pea chapter 5 says, and the Rambam in Mat'nos Aniyim chapter 6 codifies, that if someone is working a field with no claim to the not-yet-reaped crops and happens to be poor enough to claim leket, then he can claim leket from the very field he's working. Since they don't mention that he must repay the field's owner for this (and I don't see it in the commentaries, either), I would hazard a guess that he does not need to do so. That's leket; while shichcha may very well be different, I have no particular reason to think so. As always, if this is a practical question, ask your rabbi.