Hi John,
I tried duplicating the effect in the Accounts (31) example. This has a procedure UpdateInvoices, which contains the LineItems browse - hence an Insert button to add line items.
However if I cancel the LineItem it does not cancel the Invoice I am updating.
So I think it may be specific to your situation. Specifically;
a) the button you are using to call the form or
b) the URL-on-Cancel that the form is set to.
If you don't figure it out, can you please post an example here of your approach, and I'll see what's happening inside that.
Cheers
Bruce