I can't believe I forgot this after all these years.
 
Normally—in the past—I would click on a track and that is that track that would play when I used a MIDI keyboard.
 
Somehow, I have gotten Preferences messed up so that every time I play a MIDI keyboard, I have to go turn off echo on other tracks and so they don't play along with the current track.
 
I have "Always Echo Current MIDI Track" on but other tracks play as well unless I manually turn them off.
 
What have I messed up?
 
Thanks.

I have "always echo current midi track" turned off by default. I enable it as required as I move between tracks.

Every once in a while it seems like I need to change a previous midi track's input from "omni" to "a random number that isn't omni" to prevent it from playing while a new track is created.

IIRC, Echo Current MIDI Track gets overridden if you manually turn tracks on. Any tracks not focused should have echo disabled to get that functionality back.

Yes, manually enabling Input Echo on a track will force it to stay on when the track isn't focused. This is useful for layering sounds. You just need to toggle echo off on tracks that have it enabled when not focused and not showing the 'A' for int he icon for Auto-enabled.