Bezier subdevision not smooth (sometimes)

[Kapistijn]

Hi,

I'm trying to subdivide a Bezier spline so that the shape stays the same.

When testing this on a spline I drew for testing purposes it works perfectly fine (the blue spline in the picture).
But when used on another spline I get some very weird behaviour (orange spline).

I've checked all the settings between the 2 splines and they seem to all be the same.
What am I missing? Any idea on where I should look to fix this issue?

Thank you so much in advance!