OpenGL on windows with Uxsms disabled causes tearing

I wrote an application for video processing and rendering.
This application renders at 45fps (which is the frame rate of the camera).
In order to reduce the application’s latency i disabled the UxSms windows service (running on windows 7 64bit).
This saved me 20-30 ms of latency but introduced significant tearing when 2 or more displays are connected to the system (dual XEON with Quadro K4000).
With a single display connected there is no issue, but once i connect a second display i get tearing even if my application is rendering to a single display. It is enough that the desktop spans over 2 displays to cause this issue.
As i thought it was a frame rate issue i split the application to 2 threads where the first one accepts the buffer from the CPU and process it off-screen and then the other thread (which now runs at 60fps with Vsync enabled) simply renders the resulting texture. This made no difference.
I then changed the rendering thread to render alternating black and white screens and i still see tearing.
The only situation in which i don’t observe the tear is when i don’t issue any additional OpenGL commands other then in the rendering thread. Even adding an upload image from CPU->GPU using PBO is enough to cause the tear to appear again.
With Uxsms enabled i can render to 3 displays and dont observe any tearing but the additional latency is too much for this application.
Does anyone have any idea how to approach this?