GH curve tween inserting extra nodes

hey guys,

has anyone come across a similar behavior?

i haven't had any issues with curve tween inside grasshopper before, but recently just creating a basic tween between first-degress polylines with identical number of nodes (=4) ends up inserting 2 extra nodes (kinks) - see attachment.

the native rhino tween command works just fine (see comparison), but of course only interpolates in a linear fashion.

any tips are appreciated

len