Sweep tool problem

 From:  Johny
1389.1 
Sweeped a triangle profile on helix rail give odd result as shown on bellow image.

Can anyone help me with this problem? Or maybe explain why this happened?

I also attached 3dm file for test.

Thanks
Attachments:

Image Attachments:
Size: 64.3 KB, Downloaded: 80 times, Dimensions: 821x553px