Hi, 

Yes.  A router can have multiple default routers , but it is not recommended to configure more than one default route on  a router. If you do so, the router will get confused during packet forwarding. So the best practice is to configure a single default route on a router.

As per your question about packet tracer , it is because of per destination forwarding mechanism of CEF. You can read about CEF forwarding.

Hope it helps.

if you have any further query , comment it.