Other specimens of that model behave normally.

Looks like 0x9f is not allowed, only REMS, very strange.

Reading OPCODES... done
        OP        Type      Pre-OP
op[0]: 0x02, write w/  addr, none
op[1]: 0x03, read  w/  addr, none
op[2]: 0x20, write w/  addr, none
op[3]: 0x05, read  w/o addr, none
op[4]: 0x90, read  w/  addr, none
op[5]: 0xc7, write w/o addr, none
op[6]: 0x01, write w/o addr, none
op[7]: 0x00, read  w/o addr, none
Pre-OP 0: 0x06, Pre-OP 1: 0x06