Created attachment 379255 [details] [diff] [review] proposed fix ExpansionDelta is supposed to return a negative number for expanded threads, but it does not for quick search db views. This causes issues when new messages arrive in a quick search db view and we try to move threads. MoveThreadAt uses the expansion delta to figure out how many children there are, and it adjusts the sign of the result if the thread is expanded (see nsMsgThreadedDBView::MoveThreadAt).
note this only affects single folder saved searches, and quick search views.
fix checked in.