The following SQL code generates an incorrect answer of three rows instead of two:

<blockquote><verbatim>
CREATE TABLE tx(id INTEGER PRIMARY KEY, a, b);
INSERT INTO tx(a,b) VALUES(33,456);
INSERT INTO tx(a,b) VALUES(33,789);

SELECT DISTINCT t0.id, t0.a, t0.b
  FROM tx AS t0, tx AS t1
 WHERE t0.a=t1.a AND t1.a=33 AND t0.b=456
UNION
SELECT DISTINCT t0.id, t0.a, t0.b
  FROM tx AS t0, tx AS t1
 WHERE t0.a=t1.a AND t1.a=33 AND t0.b=789
 ORDER BY 1;


Prior to and including check-in [93121d3097a43997] (version 3.8.3, 2013-12-17)
the correct answer was obtained.  After that, the test script above generates
an assertion fault.  At check-in [c0fa0c0e2de50d7e] (version 3.8.4, 2014-03-03)
the assertion faults go away, but the incorrect answer is returned.