It's my fault, and yes, it is a bug: component owners receive an e-mail when a new discussion has been started, which has two links in it, one "read more" and one, far more prominent, "set as resolved", so I accidentally clicked the second link, of course :(.
However, your second post allowed me to mark that one as solution, and unset it again, so all should be well :). Appologies for the inconvience.