Comment 2 for bug 1205163

My best guess at what is happening is this:

The first time we connect to the special system bus, the dbus client is not yet initialized. I can see how init_connections_unlocked() in dbus-bus.c digs out $DBUS_SYSTEM_BUS_ADDRESS for the bus connection address, but it only does this if the connections are not yet initialized, as would be the case at first.

When the second set of tests run, we've started up a new dbus-daemon, which of course lives on a different DBUS_SYSTEM_BUS_ADDRESS, however, because the client side running the tests is in the same process as the first set of tests, perhaps init_connections_unlocked() thinks it's already initialized and so does not dig out the new DBUS_SYSTEM_BUS_ADDRESS.

If so, I'm not sure what can be done, except to run the test suite in a separate process so that the dbus client side gets initialized again every time.