Hello Thomas,
You might have VLAN12 configured in the AP profile as well as an override. By running the above command, you removed it as an override by it is still available in the AP profile and will still display when you run the sh ip int br command.
I would recommend you check the profile and overrides for this vlan:
#conf t
#profile ap7522 profile-name
#show context
if it's in here remove it:
#no int vlan 12
#com wr
#show context
Go to override and make sure it's not there either
#self
#show context
Of course also make sure that the AP is not adopted by any controller and pulling this information back in.
Thank you,
Chris
Christoph S.