Disable button style is not applied when a button is disabled

If the user applies a material or texture to the disabled button style option the button will not used the material/texture that was used but will instead use the default grayed out button look.

Edit Tim L
-------------
Additional user reporting the same issue: https://answers.unrealengine.com/questions/315330/sbutton-isenabled-doesnt-take-the-disabled-button.html

1. Open the First person template
2. Create a new Widget blueprint
3. Add a button to the designer tab
4. Add the cross hair texture to the button's disabled style
5. Open the event graph
6. Set enabled to false on event construct for the button that was created
7. Open the level blueprint
8. Add the widget to the viewport
9. Play in Editor
10. Notice that the button is grayed out (as default) and does not use the cross hair texture that was applied

Expected: The button would look like the texture that was applied when disabled
Result: The button does not used the disabled style that was applied