I found a couple of blogs that I think are related in a very fundamental way.
Kin-Man writes that a goal of JSP 2.1 is to provide a unified expression language (EL) for JSP and JSF. He talks about how compatibility with previous versions was broken in a recent build of GlassFish but fortunately a fix was made available in the last promoted build .
Compatibility is and has been very important in GlassFish. Compatibility to the specs, previous versions of the product or with other tools all matter.