Fantastic tool, I use it all the time. I'm not sure whether to mark this as a bug report or feature request.
If two lines cross but originate from, or converge to, the same point, IMT does not recognize them as crossing. This makes it impossible to create some fillers (for example) for bike lanes in a rounabout that merge.
In the image below, the lines' common origin is circled, and where they cross is marked with arrows.
