Unable to change source on a cloned assertion

Cloning one assertion from one testcase to another works fine, the source is marked as DELETED ELEMENT, right-click and open up
change source and property dialog, choose source and property but the OK button doesnt take the changes or make the dialog go away
leaving cancel as the only option. Is there some secret magic to cloning assertions that needs to be done?

Tried 4.6.x and 5.0-beta, both free and pro gives the same result.