the j/k/c/etc. keyboard navigation doesn't play well with mouse navigation: if you click into a file (other than the commit message, obviously), and then use the navigation keys, they'll still operate inside the commit message. when you use w/q to navigate between files, it works.

on a related note, the need to use w/q (rather than j/k simply moving across files) in the diff-all screen is entirely counterproductive.
also, it makes no sense at all that hitting r in the combined screen jumps to the normal review screen instead of to the cover message edit which already is on the page.