I had occasion to use the Envelope Deformation Effect yesterday on a rectange (well, it was more complicated than a rectangle, but it happens for a plain rectangle), and had ... unexpected results.

Try this...

Make a rectangle (horizontal format).
Convert to path.
Go to the Path Effect Editor.
Add Envelope Deformation.
Select the "Top Bend Path" node tool.
Select the top segment of the rectangle.
On the toolbar, click the "Make selected segments curves" button.
Change the segment to an arch shape (raise the center).

Everyting is fine for the top segment, but the side segments get
a wobble in them, even towards the bottom of those segments.

Is this expected? If so, why? Or am I doing something wrong?
This behavior makes the effect useless for just about any
application I can imagine using it for.

Looks like it might be considered a bug.

It seems that the path effect is trying to maintain the 90deg angles, so as you deform the top curve up the sides get the wobbles.

A kind of workaround is to add two more nodes just inside the two end nodes on the deformation curve. That seems to minimize the sidewall deformation.

-Rob A>

Thanks! I'll check if it's been reported when I have some time.