MrJoes/sockjs-tornado — comment on commit 3978a6377d1af085467aaf026ff6915815364344
File:  line 0
By MrJoes:

Did you see any server-side exceptions?

Because it should always call on_close for websocket connection if underlying TCP connection was closed. For streaming transports it will close long running connection if user came with HTTP/1.0 - it is new requirement in sockjs 0.2.

Anyway, try updating - there were some additional fixes and see if you can reproduce the issue.