I did a upgrade on a Nexus 7000 from NX-OS 5.1(3) to 6.1.4. When I finished the upgrade I saw a lot of problems with vPC and the Nexus stoped his communication with the other one. I did the downgrade and the problem continued to happened.
After some verifications I saw that the Nexus has erased all vlans on the vlan database file starting at 2000 and has configured the native vlan, that was erased too, as 2000.
We configured again manualy the vlans on version 5.1.(3) and the problem stoped.
Does anyone here have a clue about why the Nexus did this?