I face a strange bug on ATI cards on ubuntu.
I setup the clamping options like this:
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
and I expect to see the edge lines repeated whenever I used a texture coordinate outside [0,1]. However, this is what I get when rendering a full screen quad using a texture containing 4 colored squares (what u see in the middle) with texture coordinates from -0.1 to 1.1:
So it seems like the edges are indeed repeated but somehow faded out.
Next I attached a screenshot of the same aplication on a NVIDIA card (apart of the graphic card all the other conditions are the same):
Here it is impossible to notice the edge of the texture, as expected.
Setup: ATI HD 5870 on Ubuntu 10.04 x64 with ati-driver-installer-11-5-x86.x86_64.run. Same bug also on ATI HD 6870 and also with ati-driver-installer-11-2-x86.x86_64.run