The implementation of the manifest expression parser is such that certain syntax errors may be ignored - see bug 932552 comment 0 for more detail, and bug 922581 comment 3 for another creative technique (ab)using this. This is bad as unintentional syntax errors may cause tests to be skipped when they should be run. Note also that as per bug 932552, the ability to use '# comments' in such expressions happens to work due to this, but the ability to have '#' comments is now officially a desirable feature, so if this bug is fixed, the ability to have # comments must be retained.