When a user specifies in his design that a permanently 3-stated output is desired, the software implements this using an Open Drain configuration. This is incorrect, as the output should always be 3-stated, and not be dependant on an input.
This bug is present only when targeting a CoolRunner-II CPLD.
This problem has been fixed in the latest 6.3i Service Pack available at:
The first service pack containing the fix is 6.3i Service Pack 2.