Losing static ip address

[Jeff <debian@waysoft.com>]

Running Debian etch without problems for some time - in a simple setup 
connecting via a static local ip address (192.168.0.10) through a NAT 
DSL (Linksys) "router."  Recently, though, and seemingly ad-hoc, the 
Debian box has been losing its static ip and picking up a dynamic ip 
address (from the DSL router's DHCP server).

From /etc/network/interfaces...
auto eth0
allow-hotplug eth0
iface eth0 inet static
        address 192.168.0.10
        netmask 255.255.255.0
        network 192.168.0.0
        broadcast 192.168.0.255
        gateway 192.168.0.1
        # dns-* options are implemented by the resolvconf package...
        dns-nameservers 208.201.224.11 208.201.224.33
        dns-search localdomain

I can restart the network, and the static ip gets restored - only to be 
dropped again at some unpredictable time (usually seems to happen only 
after hours or days have passed).

Any ideas as to why the static ip is being dropped and replaced by a 
DHCP call would be much appreciated.

Jeff