"ORDER BY" failed when using "LEFT JOIN"

The following SELECT returns no record:

SELECT * from
((t1 LEFT JOIN t2 on t1.f1=t2.f1)
LEFT JOIN t3 on t1.f2=t3.f2)
ORDER BY t1.f1

However by getting rid of "ORDER BY" clause:
SELECT * from
((t1 LEFT JOIN t2 on t1.f1=t2.f1)
LEFT JOIN t3 on t1.f2=t3.f2)
will return all the records.

Why? Please advise.

Not positive on this one, but there may be some restrictions on using things like ORDER BY and GROUP BY on left joined queries, as there's a risk that there could be NULL values floating round in funny places (e.g. in your example, you may have a bunch of t1.f1 values with no corresponding t2.f1 values). This doesn't entirely make sense -- you may have a hit a bug -- but it might offer some reason as to why the bug is there. Get onto one of the MySQL mailing lists and pose your question there.