well, for the "slowy" part, I think it's because Khaled actually 'coded' /drawrot, which implies a lot of calculus (1 per pixel of the rotated surface, with the use of trigonometrics functions). that's a supposition, though.
i noticed this bug too, long time ago : when i rotated tiles by 90°, a black line appeared on one of the side. quite annoying for map drawing engines... /drawrot looks like some kind of "unfinished" command.
