failing multiple selection

override_add.html

        <label class="control-label" for="channelselect">Channels</label>
        <div class="controls">
            <select name="channels" id="channelselect" multiple="multiple" style="height: 150px;">
                {% for channel in channels %}
                    <option value="{{ channel }}">{{ channel }}</option>
                {% endfor %}
            </select>
            <p class="help-block">Channels on whih keyword should be overriden</p>
        </div>