When I try save attribute with two same values. I got error - The value of Admin must be unique.
I checked M1. M1 allows you to save attribute with same values. It is ok, because table
eav_attribute_option_value has auto increment field
value_id, and you can save two same values, but they will have two different
value_id and table
eav_attribute_option has auto increment field
option_id and will save two different values too.
In M2 added new class
vendor/magento/module-catalog/Controller/Adminhtml/Product/Attribute/Validate.php which purpose - checking value is unique or not.
Who can explain, for what was to be implemented this checking?