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I've just added a new test for reproducing this to the
test-suite in the roundup CVS. Can somebody with mySQL 5.0
installed verify that the suite really fails the new test
with mySQL 5.0, I've got only 4.1 to test and this does not
fail. To run the new test:

- Get roundup from CVS
- In the checked out repository run
  python run_tests.py -vv test \
  '^testFilteringMultilinkAndGroup$'

this test produces a query very similar to the failing query
in the original report, so it should fail with mySQL 5.0