The opb_pci_v1_02_a bridge incorrectly asserts opb_timout on the next read address submitted to the bridge after a Master Abort transaction has occurred. The test bench performs an OPB to PCI burst read where the first address at offset 0x00 is set up so that the PCI Target does not respond, which forces a Master Abort condition.
This problem has been fixed in the latest EDK 8.1i Service Pack, available at:
http://www.xilinx.com/xlnx/xil_sw_updates_home.jsp
The first service pack containing the fix is EDK 8.1i Service Pack 2.