Maybe there's a simplest way of reproducing this defect, but here's how i do:

1. Select an article which contains an attachment and do a "save article
as...". Select a folder and hit return.
=> The article attachment is saved, but the article itself isn't displayed.

2. Hit return (to display the article in the body pane). The article has to
be selected in the header pane.
=> Pan displays the "save article as..." window.

3. Close this window by hitting the escape key
=> Pan saves the attachment once again