I posted https://github.com/explorigin/Rocket/issues/1#issuecomment-3648126- I suspect it is an interplay between timeouts and sendall(), though I can't really prove it (and I can't reliably reproduce this either right now). Also some characterization about when this happens to me (slow links, dependency on chunk size, etc).
TL;DR: I think it is impossible to use sendall/write reliably with Python 2.6's socket wrapper if there's a chance for a timeout (Not sure about earlier versions). Unfortunately, Rocket seems to use sendall/write a lot. I'll be able to test this more next week.
