The fix for   Bug#18946: Test case rpl_ndb_ddl disabled   pushed around end of March 2007 enabled this testcase.
It was later disabled because the test failed with timeout on one testing box.
The reason for this failing test could not be found because we do not have informations about the conditions on the box during this test.
Jeb and I tried this test on other boxes and it passed.
My experience is that
- tests using NDB need in general often significant more runtime
  than comparable tests of other storage engines
- the actual load of the box where the test is running and the
  filesystem (nfs could be extreme slow) where the tests are
  executed might have a huge impact on the test performance 
  (runtime * 2 till 3)
- there are sometimes problems with the ports most probably
  caused by OS properties (NDB+RPL need many ports) or
  parallel tests accidently running with the same ports.
AFAIK these are the reasons why the NDB tests fail sometimes with timeout.
Conclusion: We enable rpl_ndb_ddl again because the failure happens in rare cases
and seems not to be caused by errors within the server or test code.