Products can't be copied under some circumstances in Version 5.0
Products can't be copied under some circumstances, when there is a supplier involved.
The problem appears when template and product have different next ids, because of variants.
It is a typo introduced by a backport including new technology which can't be handled:
https://hg.tryton.org/modules/purchase/rev/c43a5ec13cf7
https://codereview.tryton.org/315221002/patch/311421002/309521002