Originally Posted by mjtaylor

IME, Google uses the most relevant description it can find for the search term so it may well ignore an updated description tag if it has indexed something else that seems a better match for the query.

This is the sort of thing we tend to overlook when we consider Google (as we mostly tend to complain). Google is trying its best to return the keywords in the description because it knows that makes it more likely to please the searcher. Google is trying to return the most relevant results.