A problem exists with the 10 Gigabit Ethernet MAC v6.0 Core's example design in which the FIFO can lock up if short frames are passed into the FIFO. Both the transmit and receive FIFO fail to correctly handle short frames.
The problem is with the example design only; this is not a problem with the actual core itself.
A patch is available to resolve this issue.
To obtain this fix, install the patch that is available in the LogiCORE 10 Gigabit Ethernet MAC v6.0 Core Release Notes and Known Issues Answer Record (Xilinx Answer 21046), and then regenerate the core.