Comment 12 for bug 319710

Judging from the log given by Markus in bug 318112, I believe this is a threading problem. httplib2 is not thread safe:
if you write a multithreaded application using launchpadlib, each thread needs to have its own Launchpad object.

Basically, if two threads try to make a request simultaneously there's a good chance httplib will raise CannotSendRequest. httplib2 will try to make the request again, without re-signing it, and you'll get a 401. I don't have a picture of exactly how this works, but unless you have counterevidence I think it's very likely this is the problem.