Erika When pixel grid is on and attachment highlight smoothing is off, the attachment highlight doesn't match the image. The attachment highlight should follow the image pixels, since I can't think of how highlighting the non-pixel grid position would benefit a user.
We've fixed it in 4.2. The old behavior (notice the highlight pixels are rotated and don't match the image):
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After the fix:
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Zoomed out after the fix:
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