It also appears the "stop on playback" zoneswitch rules don't work perfectly with WDM (i.e. they don't always successfully stop playback in the IPC zone).
I installed build 25 yesterday and gave the new WDM feature a try. I added a "Windows" zone to the top of the list, and tried adding some "stop other zone" commands to the zone definitions.
My Windows Scheduled Tasks runs a batch file every morning:
mc20.exe /play "C:\blahblah.wav"
mc20.exe /append TREEPATH="Playlists\Smartlists\Morning"
This has worked flawlessly every morning for years (I've changed 18 to 19 to 20).
For the first time ever, this morning there was no sound - because it was playing in the Video Zone which was the last active zone last night (watching the local news & weather).
This is the same intermittent problem I've reported before. (The .wav file is not in the Library. As mentioned before I play plenty of files not in the Library, because they are temporary - a good example being last night's local news & weather.)
It is hard to pin down because it is intermittent, but at this point, I'm 90% sure that the problem goes away when I remove ALL "stop other zone" checkmarks.
I suspect that the bug is in the "stop other zone" code...