winword is freezing after pasting from followed by closing powerpoint on Windows 10

With 'Analyse wait chain' from task manager, you can see that winword is still waiting for powerpoint. Even the powerpoint has been closed (by clicking the x on top right of its window), there is still a powerpoint process running (not seen in 'processes' list, but in 'details' list). This looks like a 'bug' of powerpoint 2016. If you close powerpoint file by Ctrl+F4, then close the powerpoint app, everything is fine. If you close powerpoint app by Alt+F4, you have the same problem.