PE R720 PSU mismatch issue

Hi-

We had a PSU go bad in one of our R720s.  The server was reporting a mismatch with the good PS flashing green, and the bad PS flashing amber.  Server administrator reported PS1 in a good state, and PS2 critical with the status "Presence Detected, Configuration Error".  

We replaced PS2 (PN: 05NF18) with an new unit (PN: 09PXCV).  Both part numbers are supposed to be the same manufacturer (Delta) and use the same firmware.  After hot swapping the PSUs, we still get a PSU mismatch.  However, this time both PSU modules are flashing green lights.  PS2 is still reporting as critical with the status "Presence Detected, Configuration Error".  The only difference I can tell between the 2 units, is that the firmware on the 2 units is different.  PS1 is at 07.2B.7D while PS2 is using 09.2B.80; but Dell documentations claims that a differing firmwares will not cause a mismatch scenario.

What am I missing?

Thanks!

Update: Came across a thread that states a firmware difference will cause a PSU mismatch.  This contradicts Dell documentation, but I'm going to believe it because the thread describes a situation very similar to ours.

http://en.community.dell.com/support-forums/servers/f/956/t/19630123

My new question is can I hot swap PS1 with the other new PSU we bought or will I need to schedule a maintenance windows to bring the server down?

Thanks again!