Why afterPhase(PhaseEvent event) gets called twice

[Saul Qunming Yuan]

Hi,   I implemented a phaseListener to catch phase event. However, every time a jsp page rendered from a backing bean, the afterPhase(PhaseEvent event) method gets called twice, and I get the same viewId by calling facesContext.getViewRoot().getViewId(). Any ideas what the problem is?   thanks, Saul