Redmine

File app/views/queries/_query_form.html.erb
has <fieldset id="options"
which contains <div class="hidden">.
This div should have style="display: none" to work properly with function
function toggleFieldset(el) {
var fieldset = $(el).parents('fieldset').first();
fieldset.toggleClass('collapsed');
fieldset.children('legend').toggleClass('icon-expanded icon-collapsed');
fieldset.children('div').toggle();
}

Explanation:
<fieldset> and <legend> works fine, beacuse they have appropriate class to be hidden.
<div> hasn't style="display: none", so jQuery function toggle() toggles "display" property opposite way.