Custom Field Order

[Geppux]

Virtuemart  3.0.18 - Joomla 3.6.5

I have this problem; I have a product with childs and every child has other childs. In the parent product I choose the color, when I chose the color it appears the child product of the choosen color with another drop windows to choose between other 3 childs with loft difference, each of those three child has a string custom field to choose flexibility and it should be at the bottom of the drop windows but it's not, it's in the middle between color and loft (you can check this product http://www.mulligan.it/en/golf-clubs/woods/cobra-king-f7-fairway-wood-detail.html ).
In the custom field area of the last child I tried to order the fields by dragging it in the right position but when I save they are mixed. The strange thing is that if the string field has only 2 variants, instead of the 3 that i need, I can order the fields to have it at bottom, You can see it choosing color blue and loft 7/8...
Any suggestion on how to solve it? I searched and I found a similar problem solved selecting "no" to the input cart of the custom field but don't work for me. Thank you.
Giuseppe

[Geppux]

If you look at the attachment you'll se on the left how I try to order the fields and on the right how the fields are ordered automatically after I saved the left order.