This has nothing to do with minimizing the window. Again when you the vm is running, and you move to OS X an you do an OS X screen grab (key combo shift-control-cmd-4) of anything and then GO BACK to the windows vm and click on anything in windows the left mouse click are being interpreted as right mouse click which brings up the window context menu for the item you click on, start menu, outlook email, etc etc.
The only way to then get the mouse working correctly again in windows is to minimize and then maximize the windows vm.
This happens on newly created windows 7 & 10 vm's, vm's that were upgraded from windows 7 to 10, windows vm that were installed in Parallels 11, windows vm that were installed in Parallels 12 and windows vm that started in Parallels 11 to 12. This has been a consistent problems from day 1 with Parallels on OS X Yosemite, EL Capitan and now Sierra.