May I suggest trying out ReactionBar, latest version is 1.1.3. I'm the author of this mod and you can find it here
http://www.wowinterface.com/download...fo.php?id=4237
ReactionBar will automagically change your actionbar page to and from healing/balance when your target changes. Works for other healing classes and also for hunters where it switches based on enemy range.
By default the Balance (offensive) page is set to page 1, so when you shift to Moonkin this one is switched to giving you the right actions.