Probably not easily testable, but I can manually reproduce it by wiggling the window after the message about setting up an xvfb shows up. (Perhaps something connected to that changes the signal mask, though it seems a bit unlikely.)
Probably not easily testable, but I can manually reproduce it by wiggling the window after the message about setting up an xvfb shows up. (Perhaps something connected to that changes the signal mask, though it seems a bit unlikely.)