not possible to use field_language for new (unsaved) entities

I ran into this problem in a use case where I have two field collection fields on the same content type, and implemented hook_field_collection_is_empty alter for both of theses fields. For each field I get field values from the unsaved field collection entity using field_get_items, but for the second field collection field_get_items always returns FALSE. I tracked this down to a static cache in function field_language, where the entity $id is used as key. The fix is not pretty, but at least small and unobtrusive, and can impossibly cause any other issues since it in effect only disables the cache for this "special" case.