Hi Armin, I see from Paolo's comment what the difference is between your shapes..

I think probably the ones on the left you did the revolve axis with one point of it snapped on to the end of the profile, and then used "straight snap" for the second point to make a vertical revolve axis.

For the other ones, it looks like you did 2 endpoint snaps for the revolve axis, so it made a solid but at a slight angle (since the endpoints are not vertically aligned I think).

That's why there are different results there. To get rid of that you'll want to get those profile endpoints vertically aligned, once the shape is set up like that then there would not be a difference between snapping to one end and then using "straight snap" or whether using 2 end point snaps.

- Michael