Associate Plugin not triggering

I have created a 1:N relation with customer to companies A plugin on assoicate is defined however when I assign company to customer plugin doesn't trigger. This plugin does trigger for any N:N relation but not for 1:N/N:1.

However when the association is defined using code it triggers plugin fine.

http://social.microsoft.com/Forums/en-US/crm/thread/9150f71c-39e3-473f-a022-ecc54ad37992