This is specific to SPv2. The current chunk raster invalidation algorithm suppose all display items are on the same composited layer, and display items moved between chunks will be invalidated in the moved-out chunk. However, for SPv2, if the chunks belong to different composited layers, we need to invalidate on both layers.

paint/invalidation/compositing/end-of-opacity-transition.html fails in SPv2 mode because of this reason.