this looks like a bug in WordPress import on WP.com -
* WP.com blog A has a post with 1 attached image
* export the blog to WordPress XML (WXR) format
* import it to WP.com blog B, marking "download attachments"
* you'll have under Media 2 copies of the image
same file imports OK on self-hosted WP.org (3.0.5)
ALSO - only image src= URL in post that has the image attached to gets updated to new URL during import, if the image is not attached to post, old URL remains (again, self-hosted 3.0.5 seems to replace image URLs in all posts during import)
The blog I need help with is l0lice.wordpress.com.