Ok, when connecting directly there is no issue. RGB switch must be the culprit. Strange though that the TT doesn't have this issue, on both internal VGA and CrazyDots card, also on the same switch. I will check the powersupply. Also that it coinsided with me connecting something to a port and at startup this happened. Sorry I took your time everyone.
Can it be that I have no resistors on the RGB lines and also not on the Mono line. In several cable guides I see this implemented. Maybe the current is to high for the switch?