Rik,
here is what I had to do.

1, 48pt line
2. Convert line to shape
3. apply 12 pt line
4. convert to editable shapes
5. with the shape editor tool select and break the 4 points, Su described.
1-5 same as Su

6. At this point more often than not I was left with 48pt line, so I set it to a 12pt line and cleared the color of the origional shape (48pt line).
7. select and delete the two smaller end lines.
8. This is where I deviated from Su's instructions. Because when attempting to blend those two lines I would get what you ge, so because they were lines I selected both and converted line to shape. Then the blend operation worked for me.

The rest was as Su said.

If Su is reading this I hope she sets me streight. Cause I don't want to be the bearer of false information.