Comment 3 for bug 349361

This happens because the DBus call to the Policykit agent uses the default DBus timeout (10 seconds I think). The applications shouldn't assume they will get a response within 10 seconds, as the response only arrives after the user typed in their password.

I can't confirm the other behaviour you describe though. For me, just closing the Policykit authentication dialog and clicking Unlock again to open a new one works for me, without having to close the application. After looking through the code, I see no reason why this wouldn't work for you.