mirror creates seam (from sweep)

 From:  olivierth
6977.1 
Hi,

I've started practicing with MoI by creating a car but I'm having some problems. I start with a sweep but once I mirror, I can see a seam in the middle. I've redone it with a simpler example and I'm still getting the same problem.

I made sure all my profiles were starting perpendicular when looking from top and front.

I've also tried mirroring the curves instead of the surface but I end up with a super funky result.

Here's the simple test: