[curt.clifton]

Originally Posted by brianogilvie

My guess is that it's because command-shift-L is the command to flag and unflag messages in Mail.app, so it brings more user interface consistency over the operating system.

True and good. But having both ways of toggling the flag makes sense to me. There is ample precedent for multiple shortcuts in OF. (For example, 'r' and Cmd-].)

I actually submitted a feature request for the tab+space behavior about a month ago. It is what I expect for consistency with check-box columns in OmniOutliner.