Adv3 bug? MultiInstances and Booths

I have a Room that includes a number of similar Booths. I’m trying to put some MultiInstance features in the Booths, but I’m getting a stack overflow at runtime. It looks like perhaps isIn(obj) of Thing and isIn(obj) of MultiInstance are calling each other circularly. I tried tampering a little bit with isIn(obj) of the MultiInstance object, but that gave a different error.
Does anyone have suggestions? Thanks!