Noticed two possible issues, one has I belive been mentioned elsewhere.
The first relates to multipart downloads. If adding more than one at a time from browser, only one seems to get in the list the rest dissapear, not even in failed.
The second relates to singlepart files, I have had on several occasion added a number of downloads from IE, many almost immediately fail, and appear in the Failed list. Double clicking them adds them back to the download list, and in most cases then download without issue. As far as i can tell there are no filters in place for the affected files. I guess its possibly a matter of timing and could be I have requested just before it has arrived on the server, but might it be something else.