I've failed to find anything this specific in previous requests, so sorry if this has been already requested.
Sometimes crashes screw up recently pending downloads. Most of the time, most people around download complete folders/albums and losing the listing usually leaving behind two folders:
*One folder with 1 incomplete file (the one that was downloading at the time of the crash)
*One folder with several downloaded files (that are complete themselves, but are just a part of the album that was downloading in the first place).
--The former are quite easy to track down and remove. But the latter stay in the complete folder littering amongst otherwise perfectly complete albums. Finding the exact same files/album after the crash to continue the existing download is often a titanic quest.
Keep the incomplete album in the "downloading" folder until all of its files (or just the requested ones) are downloaded. Then move the whole thing into "complete". This ensures that only successfully downloaded folders from any user make it to "complete" allowing the user to purge the "downloading" folder in case of a crash or the peer disconnecting/aborting, and start from the top probably downloading from someone else.
Again, excuse me if this has already been requested elsewhere.
Edited for clarity.