Mouse offset and artifacts

[Bertus]

Hi,

I recently build a new htpc, with VNC server for remote desktop via LAN. I've used the this setup without any issues with the old htpc, but now I got 2 issues with it:
- There's a constant ghost pointer constant at a horizontal and vertical offset from the actual mouse pointer, and I see it flickering between the 2 positions. The offset depends on the position on the screen, and seems to be zero in the top left corner. The offset increases as I move away from the left/top side. At the bottom right corner, the 2 pointers are about 10 cm apart on my screen.
- I get to see a lost of artifact. For instance, if I close a window, some part of it disappears but a large portion remains on screen.

Some info:
HTPC: Windows 8.1 x64, running ultravnc server 1.2.0.5. I think I installed it as service. In any case, it starts automatically when windows starts
Client: Windows 7 x64, running VNC viewer 1.2.0.5.

On both sides I left the settings as default.

How can I fix this?