S40 automatic Park / ignition key not releasing

[jkt]

My S40 problem is intermittant. Sometimes when I park I cannot release the key from the ignition. I have had to start it up again, drive it around for a while and try to park again and that has released it so far. I have changed the battery, that didn't help. I have figured out that it is due to the button on the automatic shift stick being stuck (and not popping out to it's normal position).

Has anyone else had this problem? Does anyone know how to fix it? Is it a superficial problem or is it connected to something else?

Many thanks.