Margins might have been the wrong word ^^.
IIRC, we feed CRe a rectangle, computed after *our* margins are applied. That's what it uses to draw to. If *that* doesn't clamp to device's screen-size, *that* could be construed as a bug ;p. (i.e., once we blit that back to screen, the extra bottom rows are essentially "lost". Which works out okay for this purpose, but, could be interpreted as undefined behavior
).