The offset direction of curves (lines in particular) is not consistent with the curve's normal. Instead offsets appear to respond to their orientation relative to the world coordinate system - this is confusing and unpredictable.

This is related to this request 6585 -
but I would propose that rather than (or in addition to) a manually specified offset side, the default behavior of the function should be consistent relative to the curve direction.

Original report from @andrewheumann
DynamoDS/DynamoRevit#1661 (comment)
tracked internally: https://jira.autodesk.com/browse/DYN-826