all this on a GeForce 7800Thanks, so it was not just my video card that was playing tricks ;)
@AllPlease do your tests regardless of Paolo's results. The problem might be card family related. Does anyone of you have access to NV50 card (GF8XXX and up) to do these tests? The shader support has been redone for these cards and rendering can be correct for them.
Best regards, Krzysztof