The Scale box contains:

•Scale shape        default for W, H

•Move shape

•Move margin

These parameters control the way a shaped element is scaled horizontally and vertically.

Scale shape

The vertexes are moved proportionally to their position (this correspond to the previous system and it is the default), deforming the shape;

Move shape

All the vertexes except those on the left (for horizontal) or top (for vertical) margin are moved of the same amount, deforming the shape only along the left/top margin;

Move margin

Only the vertexes on the right (for horizontal) or bottom (for vertical) margin are moved of the same amount, deforming the shape only along the right/bottom margin.

Note that these settings do not make any difference if the element is rectangular.