Problem with adding product into category

[nima1024]

Hello all,
I have a product which works fine with it's specific price.
The problem is when I want to add this into another category, SQL returns this error:

INSERT INTO `ps_specific_price` (`id_shop_group`, `id_shop`, `id_cart`, `id_product`, `id_product_attribute`, `id_currency`, `id_specific_price_rule`, `id_country`, `id_group`, `id_customer`, `price`, `from_quantity`, `reduction`, `reduction_tax`, `reduction_type`, `from`, `to`) VALUES ('0', '1', '0', '16644', '0', '0', '19', '0', '0', '0', '-1', '1', '0.1', '0', 'percentage', '2019-11-07 00:00:00', '2019-11-21 00:00:00')

Duplicate entry '16644-0-0-0-2019-11-07 00:00:00-2019-11-21 00:00:00-1-0-0-0-0-1-' for key 'id_product_2'

First of all, I don't know why it should modify ps_specific_price when nothing related to price changed and only categories are going to be changed.
Second, Of course it's duplicate entry for that index key, because it has already been defined as special product.

Even when I manually delete this key from ps_specific_price, it returns the same error but the key shows again in the ps_specific_price, it means it gets added but Prestashop run the SQL command again.

Any idea on this?

Regards,

[Crezzur.com]

The error states the following:

You trying to insert a new line in MYSQL. Buth the ID (id_product) you want to insert already exist.

So you already have a product id "16644"

[nima1024]

I know how to read SQL commands and errors.

I want to know why such this happens when I want to add an existing product into a new category.