I assigned the Perimeter to Extruder 1 and the Infill to Extruder 2. Then i activated the Prime Pillar and assigned Both Extruders. The Proble is that the Prime Pillar is only using Extruder 1 by any Reason.
With the factory-file is anything going wrong. Not to find.
Anyway, I have tried it myself, the first time since nearly 3 years, I had never the idea to split INFILL from PERIMETERS by using different materials.
But I reach only the same result as you have done it. It seams that it is not possible to integrate a pillar for printing alternated and when this is right, it is another mystery with the ADDITIONALS .
When it is a real problem while the inactive nozzle is unclean, use the Startpoint close to ... (Layer menue), that will give place and time to the nozzle to furbish by crossing the infill area. Additional the setting Inside-Out will force it.