When configured with 2 extruders, the prime tower is only ever printed with extruder 1.
The prime tower is never used to prime extruder 2.
MatterSlice will print the prime tower layer, print the model using extruder 1, then immediately print the supports.
It's not splitting the prime tower, nor is it alternating extruders for each layer.
There seems to be some other weirdness in the prime tower generation as well, with it skipping several layers in a row for now reason.
Has anyone set up a successful multi material print using the prime tower?