Am I seeing things?  Or is SolidWorks?

  I cut an Acme thread into a cylindrical body using a profile and helix. (Design intent: OD is primary dimension, hence Cut vs. Sweep.)  The profile is a parallelogram - crest and root are parallel.

  When viewing the finished feature, the crest and root now appears to be non-parallel.  I spent most of an hour reviewing the Advanced Part Modeling Manual, trying to figure out what I'd done wrong!  (I've also tested a Swept Boss on a flat cylinder: similar result.)

  SW still identifies the crooked surface as a unified Face, however, so I'm going to have to trust that this is simply an illusion.

  Anybody seen similar results?