Thanks for taking a moment to comment on this issue if you can!
We've noticed the following issue. When replacing a FEX that has associated to a 5K, the serial number does not automatically change to reflect the new box (when using "show fex xxx".) In fact if you try to manually change the serial number with "fex serial abcdef" to match the actual serial number, the FEX goes offline. However if you do "show sprom fex xxx backplane" you will see in the output both the old incorrect s/n and the new correct s/n.
Has anyone tested with this issue, seen a work-around, or had any feedback from Cisco?? Thanks again, Simon