
Hm that is indeed rather interesting behavior. I haven't used Padding in a regular container myself - I normally just define the X and Y values of the controls relative to the container (or use nested, vertical or horizontal containers).
From testing, the padding properties rather apply to the Vertical and Horizontal containers in which you are not able to freely drag and drop the controls within the container. Should you want to define a padding for a regular container, you could reference the padding property in the x and y value of your controls:
//X property:
Parent.PaddingLeft
//Y property
Parent.PaddingTop
You could also create a nested container that is only as big as the parent minus all the padding values and add the controls here. Alternatively try to reach you goal with vertical and horizontal containers - these containers respond well to padding properties, but know that the functionality is quite different to the regular container.
If this solves your question, would you be so kind as to accept it as a solution.
Thanks!