You will notice that when TXEN is deasserted, ie. between frames,
> the LFSR is forced to all zeros (11 bits of value 0 expressed in > hex notation).
>
The clock input is not the MII.TXCLK but refers to the bits in the 5B code-group. This makes me believe that the TXEN is not the MII.TXEN which is only valid during frames. It is rather a global signal indicating that the transmitter is sending signals to the copper.