trying to assign product to shopper group - resets to available for all

[dsrpmedia]

hi

using j 3.5.2 / vm 3.0.16

trying to assign a child product to a specific shopper group, but the shopper group resets to 'available for all'

I am
1) opening child product
2) selecting the shopper group I want it available for
3) saving

how do I assign a child product to a specific shopper group - if I seem to be doing it right any suggestions on why VM is not accepting the shopper group designation would be greatly appreciated
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update, I just tried setting a top level product to a shooper group and got the same behaviour?!

so I went into the database to see if if would gret lucky & spot the column where a product would be assigned to a shopper group, but alas I cannot

there does not seem to be a shopper group option in 'jos_virtuemart_products'

I found a 'jos_virtuemart_product_shoppergroups' which l;ooked promising - but it an empty table

If someone could point me towards which table connects products to shopper groups, or a bit of advise on how to run a query which would add the products to the shopper groups it would be greatly appreciated