Shaped objects, i.e. the frames and the boxes that have more than 4 corners, may be scaled as any other rectangular object, but to scale them keeping their internal proportions intact, use the polygon tool .

The difference between the standard resizing and resizing with the polygon tool :

The object "1" is the original, before resizing.

The object "2" was scaled by the normal pointer.

The object "3" was scaled by the polygon tool , dragging the bottom points up.

Notice the "hole" changed its height on "2", while it remained in the original height on "3" although the object became shorter.