I installed RC1 clean, then imported all my old options.
I opened user.cfg.xml.
Right click in the Defs window for the context menu.
The top item in the menu is blank.
It should be "delete attribute" and does delete, but it is blank.
Also note that the Defs window has the age-old problem of narrow columns that do not auto-fix themselves.
If I change the width of the Defs tool window then the columns fix themselves.
See also:
https://community.slickedit.com/index.php/topic,15146.0.html