Hardware :: Momentary Blanking Of Screens With Dual Monitor Setup

I did set up dual monitors few times on few of my boxes, with 3 video cards :

Radeon 9250 AGP (have 2 of them) - with open source ATI driver
Geforce 6200 PCIE - with nouveau driver

In all cases I connect 2 LCDs. one 1440x900 or 1680x1050 to DVI and one 1280x1024 to VGA (all the cards have DVI and VGA out). The LCDs are the same ones tested with all cards :

1440x900 : Benq FP-92W
1680x1050 : Teac T2005L15 (identified as KTC2002 in xorg)
1280x1024 : Proview PQ-721KP

Tried on different boxes runnning Arch linux, different kernel / x / drivers / kde versions

Problem is - in all those setups, one monitor allways randomly blanks for a split second and comes back (incl. switching of the backlight, and displaying the "Source : VGA" or "Source : DVI" title as if it was switched off and on)

This happens randomly, but (more pronounced with the ATI cards) related to me clicking on stuff or the display changing (even if the changes are on the second screen)

With the Radeons only the monitor connected to DVI blanks. And the 2 radeons do it in different frequency, one is more often and one less

With the Geforce only the monitor connected to VGA blanks

When I test with 1 monitor (other one disabled in xorg) : Radeons sometimes still do that to DVI monitor but rare (much less than with VGA connected) (VGA monitor never blanks). Geforce does not do it at all and has problem only when 2 monitors are connected

I first thought its a hardware issue (the cards are from junk), but it happens the same with totally different hardware (exceps using same monitors) so i no longer think it is

There is nothing interesting in Xorg.0.log