Alex, please be patient. I've previously reported this as a comment to another report but I wanted to make this easier for other 600d owners to find so they can check for themselves (and confirm or deny this bug) and, again, I realize you don't actually have a 600d to test with so it may not be easy to fix (wish I had an extra one to send you 8-).
In LiveView mode or LiveV ML menu, the DISPLAY button should toggle between display modes. I've confirmed that this does not work on the jan26, feb04, and feb13 releases but it does work on the official dec22 release as well as a jan11 600d magic zoom bug fix release (https://bitbucket.org/hudson/magic-lantern/issue/954/play-mode-cannot-zoom-in-a-picture). One small detail to add, the dec22 and jan11 releases are very small (212k) where as the other versions (that don't work) are larger (~1,300k). I've no idea why the larger (presumably debug versions) don't work but I'm hoping you'll have some insight 8-).