If I do an inline rename (on a file or folder) in the file listing and then click on a different folder in the tree before leaving the inline edit box, then the rename is not applied.
If you change folder before applying a rename in the file display, the file display will cancel the rename. Push return first, or click anywhere that doesn't change folder (and doesn't close the window or tab) to apply the rename before moving to another folder.
I understand, but why does it do that? Shouldn't the rename happen as soon as the edit control loses focus? If I do this in Windows Explorer the rename happens regardless of where I click. If I specifically want to cancel an inline rename I would hit Escape.
Not a bug per se, but an inconsistency because it does not follow the same behaviour as Windows Explorer.
Opus is designed to be better than Explorer 
Opus is INFINTELY BETTER than Windows Explorer! 
We've made a change for the next beta which works how you've asked, since it's been requested at least twice now, and is consistent with what people may be used to from File Explorer.