This morning I opened up a new song that I had been working on last night.  I was working in Track View and noticed that the double arrows to open or collapse a track are missing today (the ones at the right edge of the track pane).  When I saved and closed the session they were there.  I haven't changed screensets or any of my display options.  Any idea how to get them back?

Disable "Auto Track Zoom" SHIFT+Z or in Track view View menu.

Thanks, Skook, that was the answer.  I don't remember enabling that function, but now I know for future reference.