node created timestamp changes on node edit

When an image node is edited it changes position in the gallery, and in image taxonomy listings. This is not the usual 'most recently edited' item floating to the top. The edited image simply shifts to a different place in the gallery with no apparent logic.

As far as I can tell this happens because image module sorts the images in a gallery by the node creation timestamp, and for some reason the creation timestamp is being incremented a little on editing the node. (Of course the changed timestamp also changes as expected.)

Here's and example.
Lets take this gallery http://sphop.perlucida.com/image/tid/62

And change the title from sphp_2002_061_henk.jpg to Seagulls on this image:
http://sphop.perlucida.com/node/322

Prior to the change we have the following (info extracted from the db):
nid: 322
title: sphp_2002_061_henk.jpg
created: 1117550744
changed: 1117550744

And the image is listed between sphp_2002_062_henk.jpg and sphp_2002_060_henk.jpg as you'd expect.

We change the title and image moves to appear between sphp_2002_067_henk.jpg and sphp_2002_066_henk.jpg as you can see:
http://sphop.perlucida.com/image/tid/62?from=12

The db now gives:
nid: 322
title: Seagulls
created: 1117550756
changed: 1117558316

So, why does the created timestamp change at all, and can I stop that happening?

I should say that the images in the gallery were initially imported using import_image.module - but I don't see what this could have to do with that.