External Screen and Yosemite

Hey Guys. i got a macbook pro 13 retina that i have hooked up over hdmi to a samsung screen , 27 inches nothing special.

My laptop never experienced any sort of crashes up until i started to use the external screen , I've used yosemite for like 3 months before i attached the external screen.

It all started with random logoffs , followed with application crashes (Chrome and skype) and now from time to time i can't log in after the screen saver kicks in .. when i unplug the HDMI cable all returns to normal.

I know I'm not providing any logs of anything etc etc .. but just wondering if somebody it's experiencing the same problem. I'm about to do a clean yosemite install as the last time i did an upgrade from the previous OSX version.
Any ideas?

on the samsung.

I read yesterday that for some folks this was fixed on 10.10.2 .. not my case.
But also that a custom color setting might cause this ... and i had a custom color setting on the samsung screen.. I'll keep you posted.

Thanks!