It seems that the links to confluence attachments are not permalinks (stabe links).

Example:

https://example.com/download/attachments/116065791/file.pdf?version=1&modificationDate=1361208962871&api=v2

Instead they should be like

https://example.com/download/attachments/116065791/file.pdf

And obviously, uploading a new version of an attachment should not change its permalink.

That's an essential feature for any HTML application. By not conforming with this Confluence is breaking HTTP standards and making indexing and search much harder.

Also, the same design flaw does break lots of links from other web applications (when the attachment is updated).