@jordikt - That is the same bad behavior that I'm seeing.
@andrew_rundquistlaw - The submenu itself works fine once created or imported (I was able to add items to my original menu by dragging items from the parent view), it's just the UI for managing it that's glitching.
Fyi, I'm also having an issue using the "Custom Move / Resize Window" as an action with my floating menu that I posted a new topic about (I'm assuming that issue isn't directly floating menu related, though I haven't tried it from an alt trigger yet either).
EDIT: Just saw jordikt's parallel reply. Double-clicking the trigger does work for me to, it's just the 'Open Selected Group' button that's broken.