Currently when using auto-grouping, the list is ungrouped each time a window is closed, and then possibly re-grouped on the next allocation - as a result, there is a brief "ungroup flash" if the list is supposed to remain grouped. Avoid this by computing the width the ungrouped list would have rather than by actually ungrouping it. https://bugzilla.gnome.org/show_bug.cgi?id=738286