Yeah, I mean Cmd+I, as per Boot17. Sorry for adding to the confusion.
I think I have started figuring out the problem. I type with the Dvorak keyboard layout (rather than the standard Qwerty). I just tried switching back to Qwerty, and both Cmd+I and Cmd+U DO work with the normal Qwerty keyboard layout.
Cmd+I and Cmd+U work just fine in the Dvorak keyboard layout on other apps (Notes, Pages, Mail, Microsoft Word), so it appears to be an Evernote-Dvorak problem. Can someone check to see if they also have this problem with the Dvorak keyboard layout on a Mac?