I am using Odoo v8 community version on (bitnami) virtual machine

I have created a custom field [name: x_Task_Status, type: Selection (Open,Completed)]. When I add it to the Search view, the result is shown as

Group
  Completed (0)
  Open(0)

When Directly searching for Open Task Status (or Completed Task Status), there are results shown. Just not working when i try to group then in one view.

Here is my project.task.tree xml:

<?xml version="1.0"?>
<!--Zohair: Replacing x_start_date with x_Planned_Start_Date-->
<tree default_order="x_Planned_Start_Date asc" fonts="bold:message_unread==True" colors="red: x_Planned_Start_Date and (x_Planned_Start_Date &lt;=current_date) and x_Task_Status=='Open'" string="Tasks">
                    <field name="message_unread" invisible="1"/>
                    <field name="sequence" invisible="not context.get('seq_visible', False)"/>
                    <field name="name"/>
                    <!--Zohair: Change Project heading to PO# by adding string="PO#" to the "project_id" filed attributes-->
                    <field name="project_id" invisible="context.get('user_invisible', False)" string="PO#"/>
                     <field name="partner_id"/>
                    <!--Zohair: Replacing date_start and date_end with x_Planned_Start_Date and date_deadline-->
                    <field name="x_Planned_Start_Date"/>
                    <!--Zohair: Change Stage heading to Task Status by adding string="Task Status" to the "stage_id" filed attributes-->
                    <!--Zohair12/16: removing stage_id usage and replacing with x_Task_Status-->
                    <!--field name="stage_id" invisible="context.get('set_visible',False)" string="Task Status"/-->
                    <field name="x_Task_Status"/>
                    <field name="user_id" invisible="context.get('user_invisible', False)"/>
                    <field name="delegated_user_id" invisible="context.get('show_delegated', True)"/>
                    <field name="total_hours" invisible="1"/>
                    <field name="planned_hours" invisible="context.get('set_visible',False)" groups="project.group_time_work_estimation_tasks"/>
                    <field name="effective_hours" widget="float_time" sum="Spent Hours" invisible="1"/>
                    <field name="remaining_hours" widget="float_time" sum="Remaining Hours" on_change="onchange_remaining(remaining_hours,planned_hours)" invisible="context.get('set_visible',False)" groups="project.group_time_work_estimation_tasks"/>
                    <field name="date_deadline" invisible="context.get('deadline_visible',True)"/>
                    <!--Zohair: Hide progressbar widget-->
                    <!--field name="progress" widget="progressbar" invisible="context.get('set_visible',False)"/-->
                </tree>

Here's my project.task.search.form xml:

<?xml version="1.0"?>
<search string="Tasks">
                    <field name="name" string="Tasks"/>
                    <field name="categ_ids"/>
                    <field name="partner_id"/>
                    <field name="project_id"/>
                    <field name="reviewer_id"/>
                    <field name="user_id"/>
                    <field name="x_Task_Status"/>
                    <filter string="My Tasks" domain="[('user_id','=',uid)]"/>
                    <filter string="Unassigned" name="unassigned" domain="[('user_id', '=', False)]"/>
                    <separator/>
                    <!--filter string="New" name="draft" domain="[('stage_id.sequence', '&lt;=', 1)]"/-->
                    <!--separator/-->
                    <!--filter string="New Mail" name="message_unread" domain="[('message_unread','=',True)]"/-->
                    <group expand="0" string="Group By">
                        <filter string="PO" name="project" context="{'group_by':'project_id'}"/>
                        <filter string="Task" context="{'group_by':'name'}"/>
                        <filter string="Assigned to" name="User" context="{'group_by':'user_id'}"/>
                        <!--filter string="Task Status" name="x_Task_Status" context="{'group_by':'x_Task_Status'}"/-->
                        <filter string="Company" context="{'group_by':'company_id'}" groups="base.group_multi_company"/>
                        <separator/>
                        <!--filter string="Last Message" name="group_message_last_post" context="{'group_by':'message_last_post:week'}"/-->
                        <!--filter string="Assignation Month" context="{'group_by':'date_start:month'}" help="Creation Date"/-->
                    </group>
                </search>

Do I need to add any other parameter? How to make it work?

Note: Created a custom field for task status because I was not able to do some tasks on the original Stage field.

(question/set-color-in-tree-view-based-on-task-stage-94556)

EDIT:

My Field is x_Task_Status. I just corrected the xml as well. ( I was trying with _id just to check if its an issue with field type). But no, its not working with either.

EDIT #2:

Adding the full xml above