You get typecast if you stay so long in a role no-one can see you as anything else, no matter what your talents are. Pilots are as prone to this as actors - and instructing is the role many of those get stuck in.
It doesn't happen to everyone, by any means, and you'd have to instruct for a very long time (over 5 years, say) to run the risk of being seen only as an instructor, so don't let it worry you too much. Interesting that you've noticed it at your home base; I bet most others here have as well.