Hmm.. I don't think I understand fully (pictures might help if possible). I have a toadstool that is about 1.5 years old, and it continues to grow in diameter.
I think I have heard that that toadstools can regenerate from pieces (I know the crown can, not sure about the base), so maybe you will get a new toadstool from the detached base. And if you are getting tentacles to come out of the other portion, than it seems to be somehwat happen. When mine is not happy, it does not extend it's tentacles.