You where suspicious about the mouse and driver i used; I used a microsoft mouse and apropriate driver.
Remember, the ErrorLog showed that not every doubleclick was recognized as being a doubleclick.
In the mouse-settings there is a doubleclick-test incorporated. Everytime i tested, it did work normally.
The testfolder shown did open or close repeatedly at every doubleclick. Many many times.
Doubleclicking on an Icon on the homepage screen, in order to start an app or program, always worked.
Doubleclicking a Callsign to filter in DXKeeper, always worked fine.
Nevertheless, at your proposition, i changed the mouse, now using an Acer mouse and driver.
Meanwhile, i upgraded to Spotcollector 8.9.1.
All this togheter, i cannot tell what the culprit really has been. The mouse? The driver?
But anyway, finally SC is working fine again as it did before. Doubleclick always works fine, everywhere.
Thanks for all support. I'm happy again.