First swept part I've done in SolidWorks as a self-taught hack.  I was re-doing an existing part with the same goofball problem (though with broken external references for the 3D sketch, so clean-sheet) only to find it doesn't seem to be user error.

Why in the world would the end face of a simple twist-sweep terminate with a face at some angle instead of perpendicular to the path? The bottom horizontal