The XAUI v8.1 CORE Generator GUI incorrectly allows for the MGT state machines to be selected for a Virtex-4 device.
This is done by deselecting the box next to the "802_3 State Machines" option.
This box is checked by default.
If "802_3 State Machines" is not selected, then the generated core will not function properly.
The MGT state machines have never been supported for Virtex-4.
In the next release of the core, this issue will be fixed and it will not be possible to turn off the 802.3 state machines.
This issue only affects Virtex-4 and does not affect other supported devices.