I have your magiclantern-Nightly.2018Apr10.550D110.zip build and it behaves as mk1174 describes. To be honest i don't remember the last time i used photo mode, so i don't even remember how it should behave, it displays "screan cleaning" then goes blank and requires either pressing Disp or Live View button (If mk1174 didn't pointed out as a problem, i wouldn't even considered it to be one).
Thank you for the build, going to test it.