How to avoid Xcode gratuitous edits to storyboard files?

When I navigate to one of my xib files, Xcode marks the file as touched. Undo and revert have no effect. Saving seems to do no harm, but the glitch causes me frequent additional git work.

Has anyone else seen this or have an idea about something in my MainWindow.xib that would cause it?

Edit in 2016 - still happening!