This is Sonar X3, although I've had the same problem with X2 and X1.  Finally it's annoying me.
 
I use a lot of midi files, so I'm constantly previewing them in the browser.  The problem occurs when I forget to set the Synth preview bus.  I'll click on a file and it'll preview in Addictive Drums instead of Rapture.  I'll change the Synth preview bus to Rapture.  Now, for some reason, that file that previewed by mistake in Addictive Drums, still previews in Addictive Drums.  All other files in that folder will preview in Rapture.  I haven't found a work around for this.  Ideas?
 
Thanks...Steve

This is a known bug. Completely closing and re-opening the media browser will break the MIDI loop/synth preview memory.

Thanks much.  I'll do that.  At least I know now it's not just my install.
 
Steve