Master Data Update

Hi

I am having a problem with update rules for vendors. I have extended the existing datasource to include two new fields. When running infosource to update the master data with the new fields, for some reason the update rules are not recognising that the master has changed, and so I am unable to populate the new fields in BW. I can see the new field values in the PSA, they are just not feeding through the update rules to 0vendor. Is there any way of forcing it to replace all existing master data.

Thanks in advance

Simon