Hi simba yeah like danperk writes above it seems to be a problem with the scaling rail getting confused about how to deal with the non-planar profile curve.

If you make the profile curve to be totally flat as in the attached example it should help.

Then if you want to have a slant on the end use draw in a slanted line on the side view and use boolean difference to cut off the end with the slanted line.

The alignment tuneups that Burr mentions above are also a good idea as well.

- Michael