MK4/MMU3 starts printing without priming nozzle  

MK4/MMU3 starts printing without priming nozzle

I just completed my MMU3 upgrade.  I  printed one test piece (a small 2-colour ring) and called it a day.

Next print I am attempting, I tried to set up 3 filaments for the 2 prints in the queue.  The first job is a set of four "spacers" made in PETG that would be inserted into a PLA print to help with bridging, later to be replaced with magnets.  Here's the steps I followed (by memory, hopefully I'm not forgetting something):

1. Powered on the printer, waited for everything to come up and finish homing.
2. Selected "Load to MMU (Advanced)", and asked to load PETG into Filament 3.  Pushed the filament in, it loaded correctly.
3. Selected the option to load PLA in Filament 1, loaded fine.
4. Selected the option to load PLA in Filament 2, loaded fine.
5. Sliced my "spacers" for extruder 3 using the MK4 with MMU3 profile.  Made sure that Filaments 1 & 2 were PLA, Filament 3 was PETG.
6. Sliced my next print for extruder 1 & 2 using same profile.

When I started the first print (spacers in PETG), the printer loaded the PETG filament to the nextruder, but it never probed the bed, nor primed the nozzle!  It just started "printing" the objects!  No filament was extruded for the entire first layer (small objects) and I cancelled after that.

I re-tried several times, no luck.  Then I selected "Load to nozzle" for filament 3, and the print succeeded including probing the bed and doing the nozzle cleaning in the near left corner of the print sheet.

Is this workflow supposed to work, or am I missing something?  Should I always be loading the first filament of the print job to the nozzle?

Thanks,

Mike