The serial loopback option in designs that target Cyclone IV GX devices is always turned on by default, which is different from designs targeting other device families.
This issue affects all Cyclone IV GX designs that contain GXB transceiver blocks.
Using the MegaWizard Plug-in Manager, edit the transceiver variation file for Cyclone IV GX, <project directory>/triple_speed_ethernet_library/altera_tse_altgx_civgx_gige.v. In the transceiver MegaWizard Interface, turn off the serial loopback option and click Finish to regenerate the transceiver variation.
This issue will be fixed in a future version of the Triple-Speed Ethernet MegaCore function.