Observe_field and habtm checkboxes

Is possible to assign a observe_field to an array of habtm checkboxes?

right now, every checkboxes has id like "customer[tiprod_ids][]" , but
if i create an observe field to check that id, only the first one works,
the other not :-(.

someone can help me?

Exactly same problem here. I did not find any solution.
If you find, please inform me.