Tearing on Multiscreen and 4k@60

Hi there

I have a multiscreen clone setup, with a primary 4k Monitor connected via DP and a secondary 4k TV connected via HDMI. The image is fine, but I have a tearing issue on the primary Monitor, although I configured everything possible to use the primary as a VSync source.

I activated VSync in nvidia-settings, and set the DP-0 as a SyncDevice in XVideo Settings.

But still, there are tearing artefacts on the DP image (primary), but the HDMI image on the TV is tearing free…

Just for checking, I attached two identical Philips monitors to the same graphics card, and it resulted in a tearing free (!) image on both screens…

Open questions:
Is it possible that this could be a driver issue?
Is it possible to mix DP and HDMI and be tearing free?
Is there a particular order of the connectors on the GraphicsCard, that prevent certain displays to be VSync-Source?

OS: OpenSuse Linux 64bit
GC: GTX 1080, Driver 375.20
Monitor: Philips BDM4065 40 inch 4k, DisplayPort
TV: Samsung 40 inch 4k, HDMI2