Converting STEP to BREP adds B-spline curves

[deGravity]

I created a simple converter to read STEP files and write them out in the OpenCascade Brep format. I find that when I do so, B-Spline curves that were not present in the original model are added.

Here is a gist that reproduces the behavior, along with a simple cylinder test case and the resulting output: https://gist.github.com/deGravity/4042e93907ec14082f68122f1c2c86b5

What is causing the B-Splines to be added, and is there any way to avoid this behavior?

[tpaviot]

@deGravity can you please insert screenshots, so that we can see which b-splines you're talking about