missing window border on PNG images with transparency

[vinc17]

Any news? FYI, I got this problem yesterday on a TIFF image. More precisely, the TIFF image was the result of a scan thus didn't contain any transparent pixel and the window border was visible. But when I selected View → Half Size, the window border disappeared. I don't see the point of making the window border disappear just because some internal algorithm to reduce the size apparently generated transparency (on the border?).