WARN RPC call to v.v received for connector 163 but no such connector could

Vaadin 6 / 7 / 8
1

I get two of these warnings every time a user logs into my Vaadin 7.1.7 application (ported from Vaadin 6). Clues as to what they mean are appreciated.

13:22:08.242 WARN  http-bio-8080-exec-7: RPC call to v.v received for connector 163 but no such connector could be found. Resynchronizing client. [c.v.s.communication.ServerRpcHandler]

13:22:08.245 WARN  http-bio-8080-exec-7: RPC call to v.v received for connector 163 but no such connector could be found. Resynchronizing client. [c.v.s.communication.ServerRpcHandler]
2

If anyone else runs across this thread looking for answers, see

https://vaadin.com/forum#!/thread/4320906

and

http://dev.vaadin.com/ticket/12909