Testing of patches on Mollom's DRUPAL-6--1 branch leads to very odd test results in almost 50% of all test requests currently:
PASSED: [[SimpleTest]]: [MySQL] 0 pass(es).
(example: http://qa.drupal.org/pifr/test/76304, but also many others)
When this happens, the patch is reported as "passed", however, with the addition of "zero passes", you do not know whether tests were executed at all or not.
Upon sending the identical patch for re-testing, it most often comes back with proper testing results (i.e., non-zero passes). Interestingly, even the plain branch test reported zero passes once, but similar to patch test results, the branch test result corrected itself after the next branch self-test (i.e., after the next commit).
Note that I've also encountered such odd test results with Drupal core patches against D7 (HEAD).