What were you rename settings?
Other then "renaming", were files moved?
How many files involved?
What actions did you do after the initial rename of the files?
(Worked on my end, on the 1 file that I tested with.)
undo button
You say, "button".
Which button is that?
(I might have missed it, but it would seem to be, Actions (menu item) | Undo Rename [Ctrl+Z].)