Once again I found the source of the issue this time around. DisplayFusion.exe had somehow gotten set to 'Run in Compatibility Mode - For Windows 8'. I don't think I did that, but perhaps some troubleshooter I ran caused it.
I turned that setting off and restarted DF. Not only did it solve the subject issue, but the DF taskbar is again 100% opaque.
Maybe this will help someone.
-Carey