Cannot select Tax Geography Type when creating Tax Regime

Hi,

I am trying to create a tax zone type to use in setting up a tax regime. The tax zone type I require is international and therefore according to the user guide (2-42, step 4) - "If this is an international tax zone type, leave the Value field blank and check the Zone Creation Allowed box." I follow these steps but when I try to save it, the  Zone Creation Allowed box becomes unticked. I have included screenshots of this.

The knock on effect seems to be that the tax zone type cannot be selected from the "Tax Geography Type" list of values in the Tax Regime set up screen.