Can`t uncheck all in Struts Multibox

Question

I have a j2ee application running on weblogic. I was confused with my multibox.

What I know of multibox is that the checked items will be passed as an array of strings on submit.

I don`t know why in my application it works fine when i uncheck a checkbox or more, as long as a single box remains checked but when I uncheck everything, the submitted array is the array of　the previously checked multiboxes when it was supposed to be empty.

Can you help me please?