How do I find what program is keeping the taskbar from auto-hiding?

The name says it all. Taskbar is set to auto-hide, taskbar does not auto-hide, obviously, I want it to auto-hide. Some program is keeping it from doing that. Sometimes I find the culprit quickly if the developer made something like the icon or app flash but sometimes I search for a while before I find it.

(And no, this, this and this are not answers to "what program," they are cop-outs when you can't fix the problem. I already have an autohotkey to kill and restart Explorer but it's annoying.)

Bonus points if you know the Windows message to trap to prevent a program from doing it because my next step is creating an open-source app that blocks it and auto-generates an email to the developer every time it happens.

Edit: I'm presently looking at poking around with the SHAppBarMessage function when I get time so if anyone has already tried that, a success/fail report could save me time.

Edit 2:

Still, this ridiculously persistent problem keeps popping up and sticking around after all these years. My current favorite workaround is pinning an Explorer re-launcher to the taskbar:

1. Create a bat file containing taskkill /F /IM explorer.exe & start explorer
2. Right click the bat and create a shortcut to it
3. Right click the shortcut and edit it so that instead of {path to blahblah.bat}, it has cmd \c "{path to blahblah.bat}"... (this is to circumvent Microsoft protecting you from putting what you want on the taskbar because they think you're dumb)
4. Drag your fancy new shortcut to the taskbar