Hi plish, try doing the Inset on the plain box first, and then use the Transform > Twist on that.

It looks like Inset is having some problem with generating offsets on the twisted side walls, so do the twisting last instead of doing it first.

It doesn't really take too much for Inset to get confused, it uses a combination of several offset operations within it, and that is not a very strong area of the geometry library that MoI uses currently. The people who develop the library have said that they have been working on an update to solid offsetting for a while now but it's still in progress.

- Michael