Custom Fields drop down defaults to product name, not size

[websmith]

Joomla 3.6 and Virtuemart 3.0.16

Im having an issue with the drop down display using custom fields. I have 3 custom fields set, small, medium and large, with small being the default drop down display.

Anytime I edit this product to change price, description, image etc. the default drop down reverts back to the product name as opposed to the default option size of small.

The only way Ive seen to fix this is to consciously open custom fields tab and change the first line back to small before saving and closing. This is a big pita if you are adding and editing alot of products. Im certain it must be operator error somewhere but I cant find anything relating to this.

It would be a great help if someone can point me in the right direction or point out where I made the mistake. I have a few hundred products to edit and am dreading this.

Thanks for any help.