Sometimes, auto unrar get the predicted size wrong. It's easy to see when it happens, as the progress indicator goes above 100%.
This should be a minor issue, but is the unrar destination is nearly full, partial/zero length files are written. Newsbin thinks the files are fine and proceeds to delete the tmp files. Normally Newsbin detects the disk overflow and pauses.
I can look deeper into when this happens, if you need additional information.