In trying to diagnose this, I got it running on iPad. I get a similar problem, but a little different.
Does OpenGL blend more than one pixel distance away? If I color all RGB in my image white on load (and leave alpha alone) then it works okay. But, I have my image bundler set up to add an outline around each image of the image's own color-- so that a letter in a font, say, is surrounded by a stroke of white. On iPad, each letter and image has a perfect (thin) border around the edge-- as if the blending is reaching out another pixel's distance away.
By comparison, on the Mac, only certain areas get this blending-- as seen in that screenshot above. But on iPad, a perfect halo around the rim of each letter.
Is this filtering going further than I expect it to? I'm expecting it to go one pixel out-- as in, I have a pixel that's 255,255,255,255, and it's next to 255,255,255,0, and that's next to 0,0,0,0 ... when I draw the first one, I expect it to blend with the second one, but ignore the third. On iPad, at least (retina?) it seems to involved the third.
Do I have higher-order blending on by default, maybe?
[Edit] Oh, incidentally, I have no mipmaps-- this is all for the 2D, "sprite" portion of the interface.