When adding multiple extension filters to an open dialog on Mac, the UI does not change. I am hoping, the intention with supporting a list of extension filters is to provide the end-user with a combo box containing items such as

All supported formats (*.png, *.jpg, *.jpeg)
Portable network graphic (*.png)
Joint Expert Photo Group (*.jpg)

While the first item in the list seems to be selected (the filter works), the user cannot change to another item. Maybe this works on Windows, but at least on my Mac OS Mountain Lion using JavaFX 2.2 beta build 19 the list is not shown