Michael, a strange thing again.
I make a curve, then revolve 360deg, then use shell command to make that solid that looks like a pot. Then I make a box and use boolean-diff.
Then I see these strange lines. I try to delete everything but the lines don't go away

Hmmm, somehow that is an extra surface/solid object and there is some problem with creating the display mesh for it. The missing display mesh is interfering with the selection process.

I'll investigate why the display mesh is not working for that object, but here is a method to delete it - select everything you can with the mouse, then do Select/Invert - at this point that funny object is selected even though it doesn't look like it. Now you can do delete to get rid of it.

- Michael

OK, it was a "playing with MoI" model anyway...