I just disassembled the cartridge for inspection and here's what I found:

-the press fit between the spindle and cartridge bearings is not very tight, maybe .0005" interference fit.
-there is indeed a step or shoulder on the spindle between the bearings, it is not a machined part of the spindle but a press fit ring placed at the appropriate position.
-in reference to the instructions from Phil that dictates the cartridge should be installed with the "L" in Phil towards the drive side, that sleeve is pressed onto the LH non-drive side of my spindle.

It seems that there is indeed enough force while pedaling to cause the spindle to move towards the drive side. This leads me to believe my cartridge was assembled incorrectly from the factory, that pressed on sleeve should have been on the drive side of the spindle, thus preventing the movement I experienced.

I've re-assembled the cartridge with the sleeve positioned on the drive side of the spindle (just flipped the spindle around). I'll ride it and see if it stays put this time.

Thank you all for being patient with me and my apologies for being so argumentative in dealing with my frustrations.