Hi Peter,
the module mounts a PIC MPU that in the module reset sets MAC address and other few registers ([url]Disable PIC on WIZ550io]) and is for this reason that then responds to your simple ping but then you have a fixed address and to change it you need to set the module again.
To use the module then as a server or client must set its registers to use it then you need something that “speaks” with the module through its SPI.
To give you just one example… to get a dynamic address via your DHCP server you must set many module registers and not just make a reset.
I do not know the hardware you’re talking about but if this happens it means that someone performs the requested operations.