2006 Jetta TDI key problem

Got a strange problem I need some help and info on. I drive the car, stop and take the key out, the motor shuts off, but the car acts like the key is still in the ignition and the key won't go back in. Anybody ever have this problem? It takes some time but eventually the key goes back in and everything is fine for awhile. It's starting to get harder to get the key to go back in and I'm afraid that eventually it won't go. Thanks for any help you can offer on this.