I haven't been able to reproduce the "can't delete bug" in the current dev build. I think I must have fixed it as I've been tweaking the menubar editor over the last day. Keep an eye on this in the next build please.
I removed the "Rename" option from the contextual menu for menu handlers as you shouldn't be able to rename them from the member inspector as they are essentially event handlers. You need to rename in the menubar editor instead.