Custom sort order on product variants not working?!

Hi,

i habe a custom sortorder in product variants
http://screencast.com/t/YoyhF2ItGP

but on the product screen, the custom sort order ist ignored.
http://screencast.com/t/goLXt0dnx

i use WP 4.6.1 with WC 2.6.4.

is this a bug or have i fail to see an option for that?

Frank