Imagine that you create multiple relationships between Accounts and Contacts. This will create several lookup attributes on the Contact entity which may be added to the Contact form.
When a new contact is created within an Account all the lookup attributes will be populated with the name of the Account. Often this is not desirable but according to this article, http://support.microsoft.com/kb/946599, this is by design.
if (crmForm.FormType == 1)
crmForm.all.new_lookup1id.DataValue = null;
crmForm.all.new_lookup2id.DataValue = null;
// and so on