Sometimes, the majority is not enough to revise a law. This happens when the revision is close to the last revision (less than 30 days). At these cases, more than a simple majority is needed.
For your convenience, every voting states the exact votes needed to pass the revision. If it needs a simple majority, it will state so. Therefore, you just need to read carefully every time for the requirements.
Since there is no manual for these yet, check this instead:
viewtopic.php?p=10417#p10417(2,000 posts!)