Menu Builder not working when no theme enabled

For one of my users, I have no UIP theme enabled. However, the custom menu I created for this user (through the UIP Menu Builder) does not work when there’s no active UIP theme. When a custom theme is enabled again, the custom menu shows correctly.

For what I can recall from earlier versions, this didn’t use to be a problem. However, I currently don’t have a site with an older installation, so I cannot test this.