I recently had an answer I gave selected as The Answer to a question. A couple days later, the OP updated his question to ask a follow-up question, and revoked his selection of my answer. I.e. my original answer is still correct and valid, but the reputation points are arguably being held hostage pending my ability and willingness to followup on this.
(I don't believe this is through any malice on the OP's part - rather, I suspect it's just ignorance of how SO works).
Are there guidelines for etiquette that apply here? Is this documented anywhere?