No that isn't weird behavior at all (disconnect phone number one, connect a second phone and the contacts from phone one go away). Think about it. Contacts are part of an individual phone, they aren't universal or added to the car. The phone that is active displays those contacts. Privacy.
Now this is odd - why would you make a "personal" call on your "business" phone? Aren't business phones for making business calls? If that's a personal number you dial, add it to the contact list on the business phone. Done and done.
I get one scenario, calling home, calling your kids, or your significant other on the business phone. There should be no earthly reason why you can't add those numbers to the business phone. Especially since they will appear in the detailed use of your "business" phone.
Tesla has exactly the same behavior - whichever phone is active, those are the contacts displayed.
2014 Platinum White FFE (Turning in mid Dec. 2016 25,000 miles)
2013 Ingot Silver FFE
2012 Titanium ICE Focus
2014 Tesla Model S 85