Using ikiwiki 3.20100815.7 on Debian Squeeze or ikiwiki 3.20100815~bpo50+1 on Debian Lenny, the [[attachments|plugins/attachment] list on an edit page all show the same (wrong) file size, which is the size of one of the files.
You can see the phenomenon on this wiki page:

-- nil

This bug was fixed in version 3.20100926: "attachment: Fix attachment file size display." done --Joey