If the FIFO has FWFT and asymmetric ports, the behavior of PROG_FULL flag is incorrect when the PROG_FULL_TYPE is chosen to be Single or Multiple Input ports (PROG_FULL_THRESH or PROG_FULL_THRESH_ASSERT/PROG_FULL_THRESH_NEGATE input ports). The PROG_FULL flag might fail to assert at the indicated threshold level.
When using FWFT with Asymmetric ports, use the constant threshold values instead of the input ports.
However, please note that the GUI allows incorrect value for minimum threshold assert. See (Xilinx Answer 24937).
This issue will be fixed in the FIFO Generator v4.1, expected in August or September 2007.