Found working solution:
in /plugins/cck_field/group_x/assets/js/script.js
add this function at the beginning:
function jformmodal() {
SqueezeBox.initialize({});
SqueezeBox.assign($$('a.modal'), {
parse: 'rel'
});
}
and execute it right before closing tags ( "});" ) of
$('.cck_button_add_'+name).live('click', function() {
...
jformmodal();
});
It seems that it must be executed after new input is added to form. I also tried with jQuery.on() but it didn't work. Still there's some bugs with image preview after adding image, but it works allright after saving the article.