This has a similar cause as RT-24607. The change to enable running the rendering and application thread in parallel split the updating of the transform and bounds (now done in updateBounds) from the syncing of the data down to the PG node (impl_updatePG) so the former can be done while the rendering is still going on.

The problem with Region is that it doesn't call updateBounds on its Shape node leading to a case where the transform is out of date when impl_updatePG is called. I verified this by instrumenting the code when fixing RT-24607. This probably is not as serious, since it is unlikely for a Region's shape to have a transform that is changing (or a transform at all, for that matter), but now that Region is becoming public API, it needs to be fixed.