check if you enter the correct address and it is not used already on the network.
as I remember if we choose the host to get the ip by DHCP if it fails it gets back to the previous config,
Maybe there something similiar happening.
Did you get the warning that you would loose connection to the host if you changed the IP address? If so did you tell it to proceed anyway and then need to add the host back into VC? If you did not tell it to proceed anyway then the change would not be made.