Realised that tal code is calling a function that I added to my
extensions/template.py file.

Add:

def set_form_wins(client,value):
    '''set client's form_wins attribute to the boolean value
       passed in.
    '''
    client.form_wins=value

to the file and add:

    instance.registerUtil('set_form_wins', set_form_wins)

to the init() function in the file.