2PC-induced lockup

The following command sequence appears to lock up the database system:

BEGIN;
LOCK pg_authid;
PREPARE TRANSACTION 'foo';
\q

After that you can't connect anymore, even in single-user mode.  The only way 
I could find is to clear out the pg_twophase directory, but I'm not sure 
whether it is safe to do that.

Should this be prevented somehow, and is there a better recovery path?

-- 
Peter Eisentraut
http://developer.postgresql.org/~petere/