Ctrl-Y is assigned to both Redo and Stay on Top.
In the File menu it shows that Ctrl-Y is for Stay on Top.
In the Edit menu it shows that Ctrl-Y is for Redo.
Of course not many people want to do both things at once
I recommend that they have separate hotkeys
Anyway right now Ctrl-Y only toggles Stay on Top. So I guess there is no hotkey for Redo in the current version?
Great software by the way