If you're explicitly keybinding the 1 button to a particular button on a bar, then regardless of what stance you are in, it will attempt to execute that action (even if that bar is hidden). The problem you are facing is you overwrote the default key binding for the action bar with your own custom ones and now it is no longer automatically paging that binding.
Lets say Battle Stance is bar 7 and Defensive Stance is bar 8 (I don't know what the actuals are, but for this example we'll use that). If you explicitly bind the key "1" to the first action button of bar 7, it will execute that action regardless of what bar you have showing in your action bar paging. You told the system, whenever I press "1", do this. Even if you are in Defensive Stance and bar 8 is displayed, you bound the "1" button to bar 7. You actually broke your default automatic key bindings for bar paging (when the bar pages, it should keep the same key binds in the same position).
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.