Comment 33 for bug 1547949

Yeah, good catch!
This video illustrates the problem.
It's tested with Mail form trunk, I just added two lines of code that print the window-width value to show if it increases or not.
    public override bool configure_event(Gdk.EventConfigure event) {

        // Writing the window_* variables triggers a dconf database update.
        // Only write if the value has changed.
        stderr.printf("event_width = %d\n",event.width);
        stderr.printf(" window_width = %d\n",window_width);
        if(window_width != event.width)
            window_width = event.width;

What is done in the video:
- open Mail two times to show that window-width stays the same
- move Mail to the right of the screen and move the slider to the right and over the end of the screen
- open Mail again two times: window-width magically increases