I can’t figure out what I’m doing wrong: when joining contours > union, I sometimes get exclusions instead of union ; the contours directions are correct though…
Good news: FontCreator 16 includes major improvements to the merge contours algorithm, and this specific issue no longer occurs there. So there should no longer be a need to first convert the outlines to quadratic before joining them.
That said, if you are still working with an older version, your workaround is a good one: convert the outlines to quadratic before using Merge Contours, or keep the overlapping contours if that works for your font.
If you run into a similar case in FontCreator 16, please let us know and upload the project file again so we can investigate it.