Offset phenomen

Could anybody explain the reason of the following strange behavior of the curve offset function:

Changing the numberf of the cutting planes the direction of some offsetted curves are in the opposit direction, like in the attached picture in case of using nr. 11 (means 9 cutting planes).

If I use nr. 14 than the result is as I have expected, but 15 is bad again, 16 is very strange.

It occures against I have tried to "directed" the section curves to the direction of the first section curve.

Thanks in advance!