In the beginning of my collecting, this happened to me a lot. I am not sure why, but it has been many years since I've noticed a stuck stem. I think that maybe it is because I wait so long after getting a new pipe before I try to remove a stem that the briar and vulcanite have time to equalize or something.
The freezer always worked for me, and pencil lead. I think that after you smoke it a few times, it may all balance out and you won't have to worry about it any more. Fingers crossed for ya. I hope it works out.