Custom Fields Order not being saved

[biltong]

A topic for this was previously created here http://forum.virtuemart.net/index.php?topic=131212.msg464147#msg464147

I'm using VM3.0.14, J3.5.1 and PHP5.6.19

I am changing the position order of various custom fields in a product which also inherits custom fields from a parent 'pattern' product.

After re-ordering the custom fields on the product edit page I click Save and the custom field order reverts to before the change.

Here are screenshots showing each stage: