The Dwarf Racial power Stand Your Ground states:
When an attack would knock you prone, you can make a saving throw to avoid falling prone.
The Invoker Stonecaller Paragon Path feature Strong Footing states:
When any attack would knock you prone, you can make a saving throw. If you save, you don’t fall prone.
Would a Dwarf Stonecaller make two saves when an attack would knock them prone?