Confluence allows attachments file names to be changed to a file name that is already attached to the page.

In 2.1.x, this led to the original attachment data being clobbered on disk, but left two attachments in the database.

In 2.2 data on disk is preserved, but as we request attachments by file name the actual attachment returned is non-deterministic.

This probably also has ramifications for attachment upgrade tasks processing pre 2.2 instances