On Control-U: I am wondering if this no longer works on your Mac because you remapped Command to Control. So I'm starting to think that there is a configuration problem somewhere on your Mac. I also pressed F2 and I was again able to edit it. I pressed Control-U and I was able to edit it. I opened up Mac Excel 2011 and selected a cell. I have just done a little experimenting and I think I have some idea of why you're having a problem.
