In v9 if you give an internal reference number to a product, and then proceed to archive the product, the field value (just the value, not the whole field) gets hidden from the product's form view.
Also, after archiving the product, it will not show up in search even when doing an advanced search with arguments "Active=False and Internal Reference=12345". This is different from v8, where a similar advanced search would still work after deactivating a product.
Is there a way to get past this feature in v9? In many cases it would be useful to search for a product based on its internal reference, even if it is archived.
Figured this one out... sort of. This only happens when you have product variants turned off and you are looking at the product template views. If you turn on product variants and then go to variant view, the internal reference shows up and is searchable as well. Not sure if this is a bug or if there is some design reason why the templates act this way.