if the group/owner are invalid it is not possible to use Cancel

If i want to change group or owner of a folder or file i do that by opening properties. If i now enter an invalid choice i get an error message when i press OK:
"Current session allow changing ownership by UID only"
Nothing wrong so far, but if i now instead press Cancel i get the same message. To cancel i need to change the group/owner back to a valid group/owner.
This can't be right? If i press cancel the group/owner should be ignored so it is possible to cancel without changing the group/owner.

I'm running Windows 8.1 64-bit and WinSCP 5.13.3

Indeed, it could behave better. But you can close the dialog using Esc key or "X" button.

This issue has been added to the tracker:
https://winscp.net/tracker/1763