the xhtml files appear with xhtml-specific icon in project tree (according to registered file extention). If you open the file in editor and in the structure view, the file structure is recognized and the jsf elements are found in this file, but the icon is not changed. When you edit the file, it immediately gets the 'jsf' icon - until the project is reopened.
If it is impossible (or too resource-consuming) to recognize the jsf contents at once, may be this functionality should be turned off at all?..