Sounds like the valve controlling the "other section" is sticking on. Could be a bit of trash in the valve. You might try opening the manual bleeder valve for a while to flush it out. Then tighten it down. If this doesn't work, you'll probably have to take the valve apart or replace it. The sticking valve keeps the other circuit on and lowers the pressure to the one not functioning.

If you don't have a leak, they a tree root could be pinching a line, or it could be valve related.

The last head on the other zone is probably just draining the remaining water in the pipe. It will take a while to quit.

Thanks guys. I notice that even when I only turn the bad zone on, water still seaps out of the other zone's last sprinkler head.