Normally software update makes all required adjustments in environment to automatically boot new version. If it did not happen it could mean either deviation from update procedure or a bug. The former we do not know (do you have any logs of this?) and if you are sure everything was done correctly, you need to open support case so possible bug can be investigated.
I don't have an experience (yet ), but from loader promt >printenv You are able to see from where ontap boots up, and with other commands you can change it. i dont think that's the final solution, but example, you can now determine, from where filer boots, image1 or image2..
i've just encountered same issueon upgrade from 8.0.2P6 to 8.1.4P3 on an HA V3270....i'm certain i followed same process on both nodes but node02 insisted on booting from image1..... although i recall it stated it was booting from image2.
Node 01 upgraded correctly and booted up off imag2...........i'd checked with version -b to display contents of image1 and image2 before initiating the upgrade from node 01 with a "cf takeover"
no force flag was used either ...........i was made aware of something wrong when i didn't need to run cf takeover -n the second time around ( the -n flag is required to overcome version mismatch on two nodes) but didn't need the -n and then realised i was still booted off 8.0.2P6 !
The fix was to manually boot_backup to get the upgraded 8.1.4P3 and then re-run "software update" to put 8.1.4P3 onto image1.
It caused a P1 as node02 was unbootable for a while but i still don't understand what went wrong. I used same process on a V3240 which was ok.
I'm interested to hear others experience of this ... not least as have to repeat same soon on FAS kit as well as the V-series we've just completed.