Windows 10 Remote Control – Start Menu opens when app focus changes from Teamviewer

I am using TeamViewer on a mac to remote control a Windows 10 laptop. When I use Alt-Tab to change the focus away from TeamViewer to another app on the controlling mac, the Start Menu pops up on the controlled Windows 10 machine.  If I change focus away from TeamViewer by mousing down to the dock and clicking on the other app, it doesn't happen.  But I never do that! I always use Alt-Tab. It's very frustrating, and it annoys the people I am helping remotely as well.

Is there any way to fix it?  I would like to be able to Alt-Tab away from the TeamViewer app on the controlling mac without the Start menu popping up on the controlled Windows 10 machine.