RM5.1: Editing a *Broken Action* cannot be Cancelled

[libra_sun_2000]

Upon editing an existing RM5.1 rule, I spotted a couple of Broken Actions:

Clicking one of them brought me to this screen:

I then change my mind, so I try to escape... However, clicking "Cancel editing action" does nothing, and I remain on the edit screen. Only clicking the dreaded "Back" button on the browser returns me to the rule.

[libra_sun_2000]

Even more curiously, if instead I proceed to assign the missing Dimmer, clicking the "Cancel editing action" button does exit the edit screen. However, the main rule window shows that assignment persisting as if I had completed the edit (i.e. behaving as if I clicked "Done editing action").