dhcp or static?

So i downloaded the newest image put it on an SD card and it works great.

now i set up a static ip address in /etc/network/interfaces

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet static

now the interesting thing

as expected i get a static ip address on a normal boot
and i get a static ip address after a shutdown now -r
but if i get a power failure and the board reboots
i get a DHCP address.
if i then issue a shutdown now -r
and reboot i get my static ip address

is there any reason this would take place ?