Help - somehow I links two tracks together (probably hit a quick key that I didn't realize) and now two of my tracks are linked together in that they are always the same height in the track window. When I resize one the other follows. I've searched the documentation but haven't hit upon the correct combination of search terms to suss this one out. Any ideas?
 
Thanks!

I think it's the auto-zoom key.  Check that out.  It's happened to me a few times and drove me nuts...

Track View View Menu "Auto Track Zoom" keyboard shortcut SHIFT+Z

That's got it - I also discovered a screen set called "Auto Track Zoom" but maybe that was unrelated.

Probably was related. The autozoom state is remembered in screensets. That's one of the many reasons they are so useful. A very powerful, often overlooked feature.