I don't know if it applies to all of them, but if you beat a challenge on one of the new high score games and try to immediately declare it by refreshing, it just comes up as "invalid score".
New update: When you beat a player challenge, it now lets you immediately declare a new challenge WITHOUT needing to refresh the score. So now you can do that even on the high-security games (which don't allow you to refresh and resubmit your score)