The reasons were 2:
 * we were adding every collection to m_expandedCollections all the
   time, which then resulted in their expansion in each slotFilter()
 * we were doing auto-expansion even in cases where collection was
   updated, not just when user typed something

(fixed in is still 2.9 for consistency with earlier commits)

BACKPORT
BUG: 300557
FIXED-IN: 2.9