Not so much a problem as an observation.
I often have a file in my download list with the status "need more sources".
In such a case, if I do a search on a keyword in the fle desciptor then, very often, the sources are found and the file will begin downloading.
If I don't do a search, the "need more sources" status persists.
Do other people observe this?
Can anyone account for it?

Yes, that usual and expected. When new sources are found, downloads that need them automatically resume.