I've discovered that returning false inside a method call from an onclick is not functionally equivalent to returning false in the onclick itself. This is causing some strange behaviour in certain browsers in certain conditions.
Some symptoms of this:
1) In Chrome and Opera, clicking the 'Download All' for an assignment does nothing; the page refreshes and you are not presented with the 'Download All' UI.
2) In Firefox (and possibly other browsers), clicking the 'Release Grades' link for an assignment will release the grades, but the checkmarks in the 'Released' column will not be displayed until a manual page refresh is done, or you click the 'Release Grades' link a second time.