The bridge is not reporting exceptions that might be queued-up in the FacesContext.
I realized this when I developed a JSF portlet that had a typo in the javax.portlet.faces.defaultViewId.view element in the WEB-INF/portlet.xml descriptor.
For example, portlet.xml had something like this:
But the file view.xhtml didn't physically exist at that path... This caused the Mojarra com.sun.faces.facelets.impl.DefaultFaceletFactory.resolveURL(URL, String) method to throw com.sun.faces.context.FacesFileNotFoundException, which ultimately gets queued-up in the FacesContext.
The solution to this problem is to have the BridgePhaseRenderImpl class iterate over the handled/unhandled exceptions in the FacesContext and throw a BridgeException if an exception is found while iterating.