After exiting the full screen with Win+Alt+M and returning back to full screen by clicking the button on the Linux taskbar the Win+Alt keys remain "stuck", so pressing any key except Alt or clicking Windows desktop shortcuts produces erratic behavior. It is only possible to "unstick" the Win+Alt by pressing Alt. Please fix. The setup is: Linux Client 16.2.0 x86, Ubuntu x86 16.04 LTS, 14.04 LTS, 12.04 LTS
The similar issue was reported more than 1 year ago... https://forum.parallels.com/threads/dont-working-text-input-after-win-alt-m.338618/