I posted on this before and thought I had resolved it, but I'm seeing it again.
When I update a zone by returning a MultiZoneUpdate from an event handler (via an ajax call), one of the components re-rendered as a result of the update has a parameter that is no longer bound. The zone update occurs in a component which declares a property that is passed as a parameter to another component. That component passes this to a third component as a parameter. After the zone update, this parameter on the third component is null. I confirmed that the accessor on the 1st component is not called when the components re-render as a result of the zone update. Anyone seen this before?