@PincoI submitted a bug via UO.com and did you see my video on the other thread? http://stratics.com/threads/since-the-last-patch-mobile-health-bars-are-screwed-up.348632/
Several changes have been made to the EC to ensure the Health Bar not updating issue does not happen. The client now checks if the "CloseButton" on the health bar is not showing and if so will close that health bar when the mobile is destroyed.
Based on the video provided re-adding the close button functionality on Health Bars will resolve your issue.