Thanks for your bug report. I inserted a few /drawsaves at different points and it looks like the issue is due to /drawrect not drawing beyond the size of the bitmap. I cannot remember the exact design decisions involved with the /draw-related features, as they were implemented so long ago, however most of them do not expand the bitmap beyond the window size. I think, at the time, the worry was that even small errors in x/y/w/h would result in an enormous bitmap that would consume all memory.
