You need to go to your keybindings in WoW and unbind the action bar paging. Just scroll down and look for the SHIFT+1 through SHIFT+6 bindings and unbind them. By default, WoW has 6 (I think?) available bars in the lower left bar, and you use either the SHIFT+# or the arrowed just to the right of the bar to access the 'hidden' bars. If you don't use this feature, you'll want to do that for all your characters.