For some reason my box creation failed, then i hit this code path:

Boxes.VMCreator.on_item_added():

if (state == DomainState.SHUTOFF || state == DomainState.CRASHED || state == DomainState.NONE)
    on_domain_stopped (machine);
else
    stopped_id = machine.domain.stopped.connect (() => { on_domain_stopped (machine); });

It took the first codepath, which warns when it tries to disconnect stopped_id.
Also, on_domain_stopped doesn't always disconnect, is that right? maybe the disconnect should be moved to the lambda?