I'd guess the regular action buttons grab their page number from their parent. It's probably defaulting to action bar 1. If you want to use those buttons and refrain from creating your own, it might be a good idea to create one bar frame for each row of buttons.
Lua Code:
parent:SetAttribute("actionpage", num)
This also means that paging on your main action bar won't work unless you use a SecureHandlerStateTemplate with a macro condition to evaluate which action page to show.