Trying to create a spiral stair, and wondering what controls the baluster spacing when Baluster Per Tread is used?

When sketching the spiral stair, the treads/risers were created according to the Tread Depth instance parameter, which measures along the center arc of the stair run to determine the placement of each riser line. I then changed the angle between each riser line to be an even 30 degrees according to a particular stair manufacturer.

When I created the railing and set it to 1 baluster per tread, the baluster does not occur in the same place on each tread, and in fact I have 2 balusters on at least one tread. Could this be because I changed the angle of the riser lines to make each tread be deeper than the dimension shown in the stair's instance properties?

*edit* and now I just placed another railing of the same type, on another spiral stair and there are 2 balusters per tread on EVERY tread of the stair, despite the rail being set to only 1 baluster per tread!