Views filters in block + add ajax behavior on 1 filter

Hello,

I have created a views with a display page and exposed filters in block.
On my home page, I have placed the filters via the block.

In this block, I want populate the value of a filter from the value of another filter (a taxonomy structure), and use an ajax behavior for this.

In a hook_form_alter function, I overrides the code of filters. But, the ajax function don't work, the form seems not to be reload / rebuild when I select an option in my first filter. Then, the second filter isn't modified.

I have tested several options / codes without success.

Here is my code:

	if ($form['#id'] == 'views-exposed-form-myview-page') {
		
		// Create the options of the first filter
		$form['field_myfieldA_tid']['#options'] = _get_associative_array_from_view(
			'views_exposed_filter_tax', // view id
			'default', // view display id
			'tid', // key field id
			'taxonomy_term_data_name', // value field id
			'All'
		);
		$form['field_myfieldA_tid']['#ajax'] = array(
			'callback' => '_update_myfieldB_callback',
			'wrapper' => 'myfieldB_wrapper',
		);
		
		// Get the current option in myfieldA
		$selected_myfieldA_id = $form_state['input']['field_myfieldA_tid'];
		// Define the options of the second filter 		
		if ($selected_myfieldA_id == 'All') {
			// Options if no option in first filter
			$myfieldB_options = array(
				'All' => t("- Choose an option in first filter -"),
			);
			$form['field_myfieldB_tid']['#options'] = $myfieldB_options;
		} else {
			// Options if an option is selected in first filter					
			$form['field_myfieldB_tid']['#options'] = _get_associative_array_from_view(
				'views_exposed_filter_tax_2', // view id
				'default', // view display id
				'tid', // key field id
				'taxonomy_term_data_name', // value field id
				$selected_myfieldA_id
			);
		} 
		$form['field_myfieldB_tid']['#prefix'] = '<div id="myfieldB_wrapper">';
		$form['field_myfieldB_tid']['#suffix'] = '</div>';

		//dpm($form_state['values']); // always empty
                //dpm($form_state['input']);  // always default value of each filter
		
	}
..................................

function _update_myfieldB_callback($form, $form_state) {
	return $form['field_myfieldB_tid'];
}

If I select an option in the first filter, I see on this field the ajax arrow, but the second field isn't modified. The form / page aren't reload/ rebuild.

Can you help me to find the problem? Do I must use and force a specific code to rebuild the form and the filters? With devel and dpm($form_state['input']), I get always the default value of each filter ("All").

Thanks for your help.