If your question contains a newline at its end, it will cause the signature to be malformed, see https://test.wikipedia.org/w/index.php?title=User_talk:Roan_Kattouw_(WMF)&diff=398947&oldid=398820. Since I don't see a reason for allowing newlines (or any other whitespace chars) at the start or end of a question (such whitespace will probably be an user's mistake rather than intention), I think we should trim question before doing all of QuestionPoster logic.

This affects mentorship questions, helpdesk question from Homepage and help pane questions.

Real on-wiki example: https://cs.wikipedia.org/w/index.php?title=Diskuse_s_wikipedistkou:Czeva&diff=17475258&oldid=17473215