When OverflowChangedTracker::Flush processes frames with an mChangeKind of TRANSFORM_CHANGED, the return value of nsIFrame:FinishAndStoreOverflow is discarded. OverflowChangedTracker assumes that the overflow has changed, resulting in an unnecessary nsIFrame::UpdateOverflow call on the parent frame. If FinishAndStoreOverflow is not reporting that the overflow areas have changed reliably, this should be corrected. If users of OverflowChangedTracker are actually intending to update the overflow of the parents, then they should be changed to explicitly add the parents to the OverflowChangedTracker.