Ah! I think we may need to let a little bit of air out of the extension.
Find the air valve and let out about 20 pounds.
It is a interesting little problem.
I'm really just taking a swag but there obviously some feature set up on the line and *maybe* we can reset it.
Try forwarding your phone somewhere on an always condition. That should light it solid. Then turn off the forwarding.
Then do the same thing for DND.
If that doesn't do it then I'm not sure even a PBX reset would resolve it since the state is saved.
I'm not even sure you could delete the key since it's 'busy'.
Ralph