While you creating new supplier, initially the field country is not indicated as mandatory field (without Asterisk). After you fill the field country, it becomes mandatory field. (Asterisk *)
Reproducing the Issue
1. Go to the Supplier Base work center.
2. Go to View Common Tasks and choose New Supplier
3. In the field Main Address, you will find the field of Country indicated as mandatory field (without Asterisk *).
4. Select a Country from the drop list and now system shows Country field as mandatory. (With Asterisk *)
Country is a mandatory field if a postal address is created, but it is not mandatory to have a postal address for an Account/Supplier.
System is working as designed.
KBA , AP-BP-BPT , Business Partner Template , How To