In the BlackBerry keyboard word substitution area there is a check box that toggles whether the word capitalization to be as input or auto. It is checked by default.
On my DTEK60 if I uncheck that option it stays unchecked.
On my new KEYᵒⁿᵉ it doesn't want to stay unchecked. If I uncheck it and go out of the app it will stay unchecked for a while then it will be checked again.