G'day,
Interesting. I had previously thought of this and checked all my tiles in GIMP to verify there is no border around the images. GIMP also reports each of my tiles is 32x32, which means my height/width SHOULD be exactly right.
What I don't understand therefore is why shrinking the height/width makes what still appears to be padding disappear.
If I set the height/width to 28x28, it works quite nicely (Didn't I tell you it was a 5 pixel pad? :) And the tiles don't look terribly smaller.
Another argument for it not being the tile is that if it WAS the tile image with the padding, making it smaller would only scale the image, not cut out any surrouding padding - so all I'd get would be a tighter/smaller grid pattern!

Nonetheless, it produces satisfactory results, so I'm mostly happy.
(Update: The image can be found: Here.)

But if anyone can explain WHY this happens I'd still be very interested.
My thanks,

JP,
-- Alexander Widdlemouse undid his bellybutton and his bum dropped off --