(In reply to comment #14)
> Thanks for the feedback. So it is a precision issue after all. If fglrx
> exhibits the same behavior, there is nothing I can do. I don't know of any
> hardware state which controls precision of texture addressing.

AMD's Windows drivers at least seemingly consistently performs
nearest-filtering with round-off-point off by a 512th of a texel. So I think
this is somehow intended (even if really unfortunate for some non-trivial
usecases).