General Description: The PROHIBIT property can be used to reserve specific device pins so they remain unused by the CPLD fitter. However, if you enable the implementation option "Create Programmable Ground Pins on Unused I/O", all unused pins, including those listed in the PROHIBIT property, are connected to the device's ground network.
You can work around this problem without the service pack by creating dummy output pins in your design instead of using the PROHIBIT property to reserve those pins.
A simple way to create a dummy output pin that remains at High-Z is to instantiate a 3-state output buffer (like OBUFE) and tie the output enable pin (E) to ground. In VHDL, you could use the following solution:
zero signal: bit :='0'; dummy_pin <= 'Z' when zero = '0' else '0';