Interaction with static IPs isn't really supported with 0.6.x well; NM
is supposed to flush the addresses on the interface when it brings the
connection up. It may be that your distro has implemented a backend
that tells NM to pull static IP settings from other distro config bits
(/etc/interfaces, /etc/sysconfig/network-scripts/ifcfg-* for example).
In that case, NM will use the static IP specified for that interface.
With 0.6.x, either you use static IP for the interface _all_ the time,
or you use DHCP all the time. 0.6.x and earlier weren't really
targetted at the static IP use-case. But 0.7 made good static IP
support an explicit goal and it'll be a lot better there.
Dan