Part of curve missing after adjusting seam

This files takes the contour curves of a cylinder and adjusts their seams.

When I next explode the contour curves, some contours miss a part of

their original length. The segment that remains is either the part between the

old and the new seam, or the inverse part.

The weirdest thing is that it appears to be random which of the contours is

having this bug and which don't. The only clue that I can find is that some

of the curves are referred to as 'circular curve', while the ones that having

the problem are referred to as 'closed planar curve'.

Does anybody have an idea what exactly is causing this behavior?