Why is the visible size of option/push buttons different?

[Tiemo Hollmann TB]

Hello,

LC 6.7/7.0 on Windows. When putting a standard option button and a push
button from the palette side by side onto a card the visible size of the
push button always is 2 px smaller, when having both button borders set to
3D. In other words you have to make the push button 2px larger as the option
button to get both the same look. When unchecking threeD border of the push
buttons, it gets the same size as the option button (with a different border
look).

Is this a bug, a wanted behavior or some compatibility heritage from old
days?

Tiemo