[imp] IMP search field

[Marco]

Hello,
I set
$_prefs['search_sources'] = array(
    'value' => '',
    'hook' => true,
    'locked' => false,
    'shared' => true,
    'type' => 'implicit');

$_prefs['search_fields'] = array(
    'value' =>  '',
    'locked' => false,
    'shared' => true,
    'type' => 'implicit');

It works. From IMP Option --> Address book I see in the right box (seleceted
address books) my shared address books. Autocomplete works with default fields
(name).

But the selection:

"Click on one of your selected address books and then select all fields
to search.
To select multiple fields, hold down the Control (PC) or Command (Mac)
while clicking."

is always empty. No fields shown, same for all address books. I can't set my
personal "search_fields" values.

Could you help me to configure imp enabling users to set search fields?

I have horde-webmail-1.2.4 edition.

Thank you very much
Regards