Mouse scaling does not respect /options/transform/stroke

To reproduce:

1. Draw a line (Shift+F6).
2. Turn off "When scaling objects, scale the stroke width by the same proportion" (at the top right of the window, the fourth button from the right).
3. With the select tool (F1), grab one of the line's corners and make the line bigger or smaller.

While the mouse button is held down, the line becomes fatter or skinnier, but when the mouse is released, the line returns to its original stroke width. This is a bug; the line should have the same stroke width during the entire operation.