images served with content-disposition: inline are being shown as attachments

Question

I've observed this behaviour on gmail and yahoo, but my concern is gmail anyway.

This is the header of the image mime part that I'm sending.

Content-Type: image/jpeg; name=image0.jpeg
Content-Transfer-Encoding: 7bit
Content-Disposition: inline; filename=image0.jpeg
Content-ID: <image0>

Gmail seems to modify the headers for some reason. This is what it appears in gmail.

Content-Type: image/jpeg; name="image-0.jpg"
Content-Disposition: attachment; filename="image-0.jpg"
Content-Transfer-Encoding: base64

Why has gmail changed the Content-disposition field? Are mail clients allowed to do that as they please? Is there no standard for these things?

Also, the Content-ID field has disappeared. I don't know why. I suspect this is causing the disposition to change to attachment.

Some help...