With standard buttons if I have OK and Cancel, with default on OK and I press the right arrow the Cancel is focused and pressing enter on the keyboard the Cancel button function
The major reason is that the Dialog normally uses BS_DEFPUSHBUTTON and BS_PUSHBUTTON to indicate this, but the ownerdraw flag is mutually exclusive to that.
Check this article: It explains the complete Background:
http://www.codeproject.com/Articles/1318/COddButton