Dhcp fallback

I have DHCP enabled and DHCP Fallbacks enabled on my RCM6750. When I power the module up it picks up an IP address just fine from DHCP. When I unplug the Ethernet cable, the app brings the interface down. When the Ethernet cable is plugged in again, the app calls ifup(). The interface comes up, but it's in DHCP fallback mode. If I disable fallbacks, then the module goes back to DHCP mode when I plug the cable in. 

I even set DHCP mode again using ifconfig(), just before calling ifup(). It still only uses fallback parameters when I plug the cable back in. It comes up in DHCP mode only on power up. 

I'll run with fallbacks disabled. But does anyone know why it works that way?

Steve