Curve Offset Issue

Hi guys,

I am having an issue offsetting some planar curves in the correct direction. I know this issue has cropped up in various forms in the past, but I have been unable to resolve it! 

I have checked:

- that the curves have the correct direction

- that the curves are planar (and all on the same plane)

I know that this issue can be fixed in this instance with a long-winded process of offsetting on both sides and then culling based on proximity to the adjacent line, but what I would like to know is where is this issue coming from and how it can be avoided.

I have attached the definition (GH 0.9.0076) below, if anyone has any ideas please let me know!

Andy