Strange behaviour of ESTK in Windows 10

The past two weeks i switched from Windows 7 to Windows 10 and am still setting up details and testing things which worked well in W7. FrameMaker 15.0.4.751 is set up with startup scripts (in particular FMgraphic.jsx). ESTK is version 4.0.0.1.

When i run one of the scripts developed in W7 times, I see a very strange behaviour of ESTK - which is reprodeable:

1. Set up ESTK to use FM-15 - it takes longer than in W7 to 'connect'
2. Run the script with F5
3. The script has completed the drawing after 6 seconds,
4. but it has not ended. The hour glass is visible until second 21.
5. But it is still not possible to start the script again - at least for 10 seconds.
6. If i want to leave ESTK with the X button, for at least 15 seonds nothing happens, then it closes (or most time it tilts).

See the vidio on my website 

BTW it is not possible to use this URL in the "Insert Video2 function of this forum - it seems that only Youtube stuff is accepted ...