Dimension Default Import (Data Migration)

I don't understand this. I have major issue with this.

I used data migration tool in all the companies for a client to import the default dimension as code mandatory

I have Global Dimension 1 Set in the Receivables/Payables as the profit center, which means they need to put the value into the header to invoice the purchase/sale

It is working but for some reason is not validating and is allowing the user to invoice without putting in profit center code on the document header ... ???????

What am I doing wrong here ... this problem has perplexed me for a long time now ... I have imported default dimension codes as code mandatory on the receivables and payables but it still allows the user to post invoices without putting in a profit center on the header of the document ... PLEASE HELP !!!