Sorry I didn't come across this earlier, but I use Listmaster a lot and didn't explore the new Multicolumn feature until just today.
When I click on the Muticolumn checkbox, it either disappears, or it won't accept the click depending on which type of field I'm doing it to. See the video below. This is on OS 10.8.5. I think I used it once with no trouble, so that must have been on Sierra...
SuperEdit Info BoxJoe