I just installed IDEA 8.1.4 and my Facelets (*.xhtml) started showing errors.
As a first example, the ui:composition and ui:include behave differently (see facelets.png attached). The ui:composition is complaining when there are two ui:define elements in a sequence and the ui:include one always wants a ui:param specified.
Maybe IDEA is more strict with its checks in the last version but in this case the XSD file should be fixed to allow syntax that is otherwise working in runtime.
As a second example, custom taglibs have problems with validation (see taglib.png attached). IDEA navigates to the authorize tag:
Here is the XSD for the custom taglib:
When used, IDEA complains that no declaration of the element autorize can be found and taglib is not a element. In this case, I cannot define well what is wrong.