When I connect using xpra 0.0.7.29 (or later) to a machine that has xpra 0.0.7.27 (or older), I get the following error:
Attached (press Control-C to detach) connection lost: empty marker in read queue Connection lost
Also I noticed once that the window I am trying to attach appears momentarily then disappears and the error message appeared.
Good catch! r270 fixes this - please re-open if necessary
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/38