This issue is now 1 year old. It would be nice, if somebody could give a
short feedback if this issue wold be fixed in the future. I found out, this issue occurs not in my local LAN, only via Internet. But the application itself is very responsive (via internet, and the connection is fast), only when moving the windows, there's a horrible slow repaint of the background.

Mit freundlichen Grüßen,
Sebastian Loncar
Geschäftsführer der Tamani UG
Mobil 0151-22389000