Agree totally.
However, the intention was to follow exactly that procedure already before, so I would assume it should have worked. But to be sure I set up a new VLAN 91 right now as per your instructions (also with only one IP in the pool with your suggestion on /30). I assumed step 5. relates to the Allowed VLANs, and to check the specific VLAN, now 91, only. This time VLAN in the device list shows up as 26. 
Edit: VLAN 26 is not among the defined VLANs.
Edit 2:
After a reboot I can perhaps see some sort of logic:
Devices on VLAN 30 gets VLAN 1 in list.
Devices on VLAN 40 gets VLAN 2 in list.
Device on VLAN 91 gets VLAN 3 in list.
Devices on VLAN 40 moved to VLAN 50 (port tagging changed) gets VLAN 12 in list, which is my 9 VLANs currently defined in Settings + the three used by the wired ports for VLAN 30, 40 and 91 above.
Devices on VLAN 50 moved back to VLAN 40 (port tagging changed back) gets VLAN 2 back in the list.
To me this looks like an index/iterator being printed instead of the actual VLAN ID. Is there perhaps some sort of array holding information on VLANs where the iterator gets printed instead of the VLAN ID?