I have searched the forums and I have yet to see this problem or a solution posted anywhere.
I have created several custom menus, hotkeyed them, and saved/stored the configuration. At first these function as they should. However, after 2-3 uses of zbrush (opening and exiting) the menus completely vanish. The rest of my customUI remains intact - only the user created menus are gone. I attempt to reload the UI and everything loads except for the menus.
The only workaround I have found is to save a copy of the customUI file to a folder outside of the zbrush directory and use this to load the UI whenever this happens. This problem has been persistent, happening 4-5 times in the last 2 days.
Any ideas?

