my best guess is the router ...
if the IP address changes at the GW1000 end, it has received a different one.
IP addresses with the GW1000 are not static, the GW1000 takes what is offered by the router, usually the DHCP server on the router, hence the router must have provided (for whatsoever reason) a different IP address. The MAC address of the GW1000 is almost impossible to change, (it might be faked though), especially not temporarily.
But you were not clear in your statements - what changed ? The IP or the MAC ? What was wrong in WS View ? IP or MAC ?
If the IP, how would the MAC "come back" after a power cyle ?
And where did the MAC change ? In WS View or in your router ?