Curious buildfarm failures

Since commit 2065dd2834e832eb820f1fbcd16746d6af1f6037, there have been
a few buildfarm failures along the lines of  -- Commit table drop COMMIT PREPARED 'regress-two';
! PANIC:  failed to re-find shared proclock object
! PANIC:  failed to re-find shared proclock object
! connection to server was lost

Evidently I bollixed something, but what?  I've been unable to reproduce
this locally so far.  Anybody see what's wrong?

Another thing is that dugong has been reproducibly failing with
drop cascades to table testschema.atable -- Should succeed DROP TABLESPACE testspace;
+ ERROR:  tablespace "testspace" is not empty

since the elog-doesn't-return patch (b853eb97) went in.  Maybe this is
some local problem there but I'm suspicious that there's a connection.
But what?

Any insights out there?
        regards, tom lane