We're seeing reports of sync loops in apps from Facebook to gmail to K-9 and on, severely impacting battery life and system resources in some cases.
The remedy, beyond what you've been doing with the forced power down, is to go into the rogue app and clear cache and data (you'll have to re-configure): menu > settings > applications > applications management.
Some users even uninstall the app(s) and reinstall.
For what it's worth, having apps configured to update or sync manually on demand seems prudent if you've seen these loops in one or more apps. It gives you more control and negates the possibility of this issue recurring.