If rogue uses stealth and first action bar changes, first button there is slot 73, not 1. Maybe there is problem with visual part of your code. Are you using something like button:GetID() to identify buttons/slots?
If you need events, there is a list in ActionBarController.lua - it maybe would be good idea to look there and inside ActionButton.lua too.
Here is exactly what you need, i think -
http://wowwiki.wikia.com/wiki/API_GetBonusBarOffset