The symtom was one of these two on upload of files only
* panic: d.nx != 0 in crypto/md5.(*digest).checkSum
* read tcp: i/o timeout
It turned out to be a combination of two upstream bugs
* 5a2187309e
* https://groups.google.com/forum/#!topic/golang-dev/0Nl6k5Sj6UU
This commit contains a work-around for the second problem, I've fixed
the first and had the change accepted upstream.