Service field is not getting blank if service offering is made blank

[Debasis Pati]

Hello All,
We have made the service field as read-only and once we select any service offering its setting the service coming from service offering table which is parent on service offering what we have selected and setting the service offering.
We had a requirement to set the assignment group if we select any service offering then itis having a logic to find the assignment group if no records then it will pass the service offering support group and will set the assignment group .
Now when i did set the assignment group i did find one out of client script is again clearing out the service offering then i deactivated the oob script which is clearing the service offering.
on change client script name- Clear Offering on changing Service

Now while testing this i encountered one issue the issue is 
if i have selected a service offering called x and its's parent y got selected as service on the form on service filed if i remove the x then it only shows service offerings which are service offerings of x only it is not getting cleared.
I mean to say when i clear the service offering its not clearing the service as we have just cleared the value and not changed the value no script is getting trigger nor ui policy to clear the service field.
also i found reference qualifier on service offering i cleared the reference qualifier on service offering field  as well but no luck.
I wonder how we will tackle this kind of situation. If we are not changing any value just clearing the value how the dependent fields or parent fields we can clear ?

@Ankur Bawiskar any idea?