I'm using Inkscape 0.91+devel r (Mar 14 2016)

To reproduce results:

1. Draw any shape

2. Add a linked offset to the shape

3. Drag the linked offset handle out or in.

Star and rounded rectangle example with linked offset here:

As you can see the results are wavey/garbagey.

Whatever changes were made to the linked offset modifier seem to have broken it pretty badly. :/

Thoughts?

-C