Hi 3DFANATIC, mirroring doesn't change the shape of a curve, so if the curve was ending in an upwards pointing direction, 2 of those mirrored will make a sharp corner.

The ending direction of a curve is defined by the line between the last 2 control points like this:





If you want it to be smooth when mirrored that means you need the 2 curves to have the same direction there, that means their end and first inside points should all be one the same horizontal line.

There are a few ways to do that, when you're drawing a curve you can use the "Perp" snap for the last point to know that it's perpendicular to a center line, or you can select the points and use the edit frame to squish them down so they're on a horizontal line, or also the Transform > Align command can do it too.

Another thing you can do is if you use Edit > Join to glue the mirrored pieces together you can select the point that's shared between the 2 segments and delete it to make it all one single segment which will be smooth.

But it's generally a good idea to take special care of the first 2 and last 2 control points of a curve you're drawing so they're on the same line if you want it to mirror smoothly.

- Michael