That sounds like a ‘buglet’ to me.
When both boxes are unchecked (which they are by default!), there is some strange, inconsistent behavior with Armatures:
When you are in Object Mode or Pose Mode, then you get: TAB -> Edit Mode (Toggle).
When in Object Mode : CTRL+TAB -> Pose Mode(Toggle).
When in Edit Mode: CTRL+TAB -> Pie Menu.
