89 Chevy Van- Ignition locked ON

Hoping someone could help. I have an '89 Chevy Van, just pulled in home, put it into park and when I went to turn it off I found the ignition was locked. I tried driving it around a bit, shifted from different gears to park etc, but it is stuck.

I disconnected the battery to turn it off, then tried to turn it back on again and it started fine, but was still locked in the ON position.

Any ideas?

Thanks.