The cropmarks on the EOS M seem to disapear when changing screens via the info button when returning to the ML screen or when returning from the playback screen.
Have noticed similar behaviour when scripting and 'got round it' by doing a scripted half_shutter press.
Does doing a half_shutter press work for you?
Unable to reproduce on other models.
Alex this is what I see in using my Focus Bar. If I clear an area of the screen, ie using color,TRANSPARENT, eg to clear something that was previously written there, then the ML cropmarks in that area do not come back unless I do a half shutter press in my script.
I've tested this in my script, ie comment in and out the half shutter press.
BTW I do all my drawing inside the display.draw() call.