Disable Post Limit?

I'm not exactly sure what the exact term for this is, but I'll explain my situation as much as possible:

So I have a few threads that get a lot of posting done in it, and when it gets to a few pages after page 67, it'll automatically break off at page 67 and start a new thread with that topic title and automatically lock the old one.

I'm not sure what that is called and I'm curious if there's a way to turn it off. It's kind of annoying seeing a thread split up in to several different ones.