The MIG 7 Series GUI prior to the v1.6 release (available with 14.2) did not prohibit memory interface pins from being allocated on the reserved PUDC_B configuration pin. Because this pin requires a strong pull-up or pull-down during configuration, it cannot be used for memory pins.
Starting in MIG v1.6, thePUDC_Bpin will no longer be used in pin allocation.
While the standard MIG flow prevents PUDC_B usage, there are some cases, such as batch mode, where the pin is allocated or passes the pin verification process. This issue will be resolved in MIG v1.7 to be released with ISE 14.3 Design Suite.