Hi @janoChen:
Your theme (or a plugin) is overriding your filter. Try increasing the priority like this:
add_filter('excerpt_more', 'new_excerpt_more',11);
Or like this:
add_filter('excerpt_more', 'new_excerpt_more',20);
And if that doesn’t work try:
add_filter('excerpt_more', 'new_excerpt_more',100);