This is with 6.62 final (build 4358), but probably with older builds and versions as well.
Just in a few short hours my Chunks folder grew from 0 (after I previously deleted all the chunks manually - today!) to 73 GB - and everything in the download list is successfully downloaded, unrarred and deleted, those chunks do not belong to something that is not finished downloading yet.
Why (so many) chunks are not deleted automatically? Seems like a bug.
To grew orphan chunks so quickly, try downloading something posted by d@mn.dymyca(DD) in a.b.tv group. Remove the two letters "y" to get the correct poster - I added them to avoid triggering hits by search engines. Besides, it is a very offensive word
BTW, I asked ages ago to add "Poster contains" into custom filters. Well, at least a few versions ago. Still not done in 6.62. Because of that, you will have to figure out yourself how to find posts by that poster
(a hint: you may search for strings containing a date, for example, 151201, or 151116, etc.
BTW-2, off-topic questions (sorry for that, but I will try to make them relevant to this topic):
1. how to specify the poster in the search string (such as the above mentioned DD)?
2. why search for 151116_ returns all the same garbage as 15116 - an underscore is not white space nor a delimiter, this search string should result (hopefully) only in the posts by the above mentioned DD ?
UPDATE: 10 GB of orphan chunks again literally in one hour. Downloading @ 270-290 Mbps