OK, Thank's Black Mariah, that answered my first question :o)

As for the other thing, I include mouse.3dm.

While I'm here, I seem to have found another anomoly. I'm getting an error in this sweep (Example2.jpg) but only when I select the outer rail first. It appears to conform to the curves when I select in the opposite order. Maintain height is switched on, the effects are greater without. For this, I attach Mouse2.3dm.