I just released an update to the KeyDB Helper. This new version will locally validate the MK, VUK, and UK and if any of those differ from the keydb entry it'll update the keydb entry in your keydb.cfg and then run the findvuk validatedisc to update the keydb. This should allow people to fix keydb entries now. Just run the disc info function against your disc.
(And yes, I could correct it easily directly in the db - but in the long run it's better to check why "validatedisc" does not work as expected to avoid the need for constant manual adjustments).
In this case, I suspect "validateDisc" did not work because the VUK value in the KEYDB entry being validated was incorrect.
Just checked my code and you're right - in case a VUK is available it's used and everything else is ignored.