Sorry if people thought I was talking about anti-aircraft fire!
The border I reported was an alpha blend of the quad and the colour underneath. In actuality the only problem is that the quad is offset by some half a pixel. It's easy enough to work round, but unexplainable behaviour and this may impact other people's code too. If you haven't done so, make sure you run your program with AA turned on on the GPU settings to be sure everything aligns nicely.
The border I reported was an alpha blend of the quad and the colour underneath. In actuality the only problem is that the quad is offset by some half a pixel. It's easy enough to work round, but unexplainable behaviour and this may impact other people's code too. If you haven't done so, make sure you run your program with AA turned on on the GPU settings to be sure everything aligns nicely.