I'm using point sprites for my particle system. Whenever I try texturing them with gl_PointCoord, all of the color for my points become red, black, green and yellow at each corner. If I replace texture2D() coord argument with gl_PointCoord in my GLSL shader, I the weird results mentioned above. If I replace gl_PointCoord with a vec2 and some random texture coords, the whole sprite appears to be affected by the correct pixel color though.

I'm also using 8-bit, GL_LUMINANCE textures since they're just used to store alpha maps.