Rhino 7.27 Line normal curve option has strange restriction

The Line command normal option has new feature: normal to curve. Unfortunately, this new feature behaves like the old surface feature - it restricts the line to two opposite directions which are parallel to the CurvatureGraph. This restriction seems to be a bug rather than a feature.

looks like its working as designed… if the curve is flat, then yes you’d get ony in/out style lines-

but if the curve is 3d, you get a result like this:
image

Not a bug. It is consistent with the usual mathematical definition of the normal vector of a curve,. This is the direction of the derivative of the tangent vector of the curve, and is the direction of acceleration of a point traveling along a curve at constant speed.
https://tutorial.math.lamar.edu/classes/calciii/TangentNormalVectors.aspx
http://web.mit.edu/hyperbook/Patrikalakis-Maekawa-Cho/node23.html

Note that if the curve is straight the normal vector is undefined. If Line with Normal option is applied to a straight portion of a curve or a line the command returns a message that the normal line is not defined.

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