We can add attachment to our post, but only if we do it on creating. After that, if we did, we are able to modify (change attachment or delete it). But if we did not, no way to add an attachment editing our post. The workaround is to post a reply - so this is not a problem so big - but it would be nice to be able to manage attachments even on post that does not born with them...

Cesare I.