Interesting: Their build server has a failing test for crypt: http://gcov.php.net/viewer.php?version=PHP_5_3&func=test...
So I would assume that this should have been caught by running the tests before making the release. Or whoever ran the tests had them passing due to build artifacts of previous builds.
Or there are just too many tests that fail regularly: http://gcov.php.net/viewer.php?version=PHP_5_3&func=test... - when you have 201 failing tests, one more probably isn't going to cause any concern.