Not a bug really. OneDev by default ignores trailing whitespaces. And white space change can be displayed if the option is set to "do not ignore":

Oh ok. Is the option new or has the default been changed? I have it on default and never seen the Content is identical message before.

Anyways, maybe the message isn't perfect. I mean it felt weird enough to me to open an issue. I am thinking of something like Only white space changes (show) with show being a link/button to reveal the diff.

This has never been changed.