MacPro lt13 4k monitor 7680x4320 res after each wakeup, s'times 1024x768

I have a Mac Pro (late 2013) with 3 4k monitors on Yosemite 10.10.2. On the right monitor Win7 runs in full screen mode. Every time the screensaver is on and I come back the resolution (normally 3840x2160, 60Hz) goes to 7680x4320 and I need to go into control panel to adjust resolution. Each time in addition, the mouse cursor becomes noticeably more sluggish which is not fixed by rebooting Win 7 - I have to reboot the Mac. I am using Parallels Vu driver.
This has been going on for over six months and I hoped it would get fixed but no luck.
If I don't reboot pretty much every day, some of the waking ups and sometimes on booting Windows 7 the resolution is 1024x768 and I have to adjust as well.
Does anybody know what to do?

 

Hello ChristophS2, please follow the steps suggested at http://kb.parallels.com/116141 and let us know how does it work.

 

Thank you, the problem is much reduced. Instead of every time it is now once a week or so.

 

Hello ChristophS2, please check your Inbox and respond, thank you.