Why do some GND (ground) pins (listed as GND in the device pinout document) on my device show discontinuity during pin to pin measurement?

Description

When measuring continuity between two GND pins on an Altera® device, not all  pins marked as GND will be connected internally to other GND pins. Sometimes they may be left floating for package migration, or physically need to be tied to GND because they are special purpose test/mode pins.