I haven't tested this bug, but it's happened to me at least twice in the past few days. Hopefully it's easily reproducible.
I queued a few downloads, deleted the current download before completion (while currently downloading), then when the next download in queue starts downloading, its parts aren't decoding for some time (seemed like a couple of minutes).
My wild guess is that deleting a current download isn't disposing of the decode thread, but like I said, wild guess.