draw selection rect only if mouse has moved

src/ui/WorldRenderer.cpp

@@ -1019,8 +1019,9 @@ void WorldRenderer::drawOverlays(QPainter& painter, const WorldCoordinates& coor
         }
     }
 
-    // Box-select rectangle
-    if (frame.isBoxSelecting)
+    // Box-select rectangle. Not drawn until the drag has moved far enough to read as
+    // one, so a plain click does not flash a rectangle (REQ-UI-MULTI-SELECT).
+    if (frame.isBoxSelecting && frame.isBoxDragMoved)
     {
         const QPoint tl(std::min(frame.boxStartTile.x(), frame.boxCurrentTile.x()),
                         std::min(frame.boxStartTile.y(), frame.boxCurrentTile.y()));