Why is there a difference in the IOF rate charged on exchange operations to my global account and to my investment account?

Following Brazilian tax legislation, exchange transactions define the IOF rate charged according to the purpose of sending the amounts to another country. 

If the objective is to invest, the IOF applied to the transaction will be 0.38%. 

You must invest the amounts of this type of exchange to fulfill the transaction's purpose properly.

If you are sending the amounts for availability in a spending account outside Brazil, the IOF tax will be 1.1%. 

In this case, you can use the amounts as you wish, whether for purchases, withdrawals or transfers.