Vat calculated incorrectly on product when added to cart (using a vat number)

[Unlimitedbul]

Preconditions (*)

1. Magento CE 2.3.1 without sample data is installed.

Steps to reproduce (*)

1. Configure tax zones and rates as follows:
   
2. Configure tax rules as follows:
   
3. Configure customer groups as follows:
   
4. Add a test product:
   
5. Set the default country (stores>configuration>general>general) to the Netherlands (other european countries should have the same problem)
6. Configure store information as follows (Make sure you use a valid european Vat number and country combination. The vat number should not contain the country prefix):
   
7. Configure customer configuration (stores>configuration>customers>customer configuration) as follows:
   
   
8. Configure Tax (stores>configuration>sales>tax) as follows:
   
   
9. Create an account in the frontend with (make sure you use a valid vat number country combination according to the tax rule setup earlier (BE vat number). The vat number should not contain the country prefix):
   
10. Enter a default billing address (make sure the vat number is the same one used in the previous step and the country should be the same as the origin of the vat number (BE in this case)):
    
11. Go to the product page of the product you added.
12. The price it shows should not contain any tax for Belgium vat validated customers (this still works as long as you have never added a product to your cart before).
    
13. Add the product to your cart.
14. Open the shopping cart

Expected result (*)

1. The shopping cart shows the same price as the catalog (no tax added to the product)

Actual result (*)

1. The shopping cart shows the price with the default BE tax (10%) added.
   
2. From this point on the catalog also shows the wrong price.
   

Workaround

Adding the following 2 lines to:
vendor/magento/module-quote/Observer/Frontend/Quote/Address/CollectTotalsObserver.php

Starting from line 105:

/** try to get data from customer if quote address needed data is empty */
if (empty($customerCountryCode) && empty($customerVatNumber) && $customer->getDefaultShipping()) {
    $customerAddress = $this->addressRepository->getById($customer->getDefaultShipping());

    $address->setCountryId($customerAddress->getCountryId());  // ADD THIS LINE
    $address->setVatId($customerAddress->getVatId());           // ADD THIS LINE
    $customerCountryCode = $customerAddress->getCountryId();
    $customerVatNumber = $customerAddress->getVatId();
}

Seems to have fixed the issue

[m2-assistant]

Hi @Unlimitedbul. Thank you for your report.
To help us process this issue please make sure that you provided the following information:

• Summary of the issue
• Information on your environment
• Steps to reproduce
• Expected and actual results

Please make sure that the issue is reproducible on the vanilla Magento instance following Steps to reproduce. To deploy vanilla Magento instance on our environment, please, add a comment to the issue:

@magento give me 2.3-develop instance - upcoming 2.3.x release

For more details, please, review the Magento Contributor Assistant documentation.

@Unlimitedbul do you confirm that you were able to reproduce the issue on vanilla Magento instance following steps to reproduce?

• yes
• no

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[Unlimitedbul]

@magento give me 2.3-develop instance

[magento-engcom-team]

Hi @Unlimitedbul. Thank you for your request. I'm working on Magento 2.3-develop instance for you

[magento-engcom-team]

Hi @Unlimitedbul, here is your Magento instance.
Admin access: https://i-23116-2-3-develop.instances.magento-community.engineering/admin
Login: admin Password: 123123q
Instance will be terminated in up to 3 hours.

[Unlimitedbul]

@magento-engcom-team issue reproduced in provided instance.

[m2-assistant]

Hi @davidverholen. Thank you for working on this issue.
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[davidverholen]

@magento give me 2.3-develop instance

[magento-engcom-team]

Hi @davidverholen. Thank you for your request. I'm working on Magento 2.3-develop instance for you

[magento-engcom-team]

Hi @davidverholen, here is your Magento instance.
Admin access: https://i-23116-2-3-develop.instances.magento-community.engineering/admin
Login: admin Password: 123123q
Instance will be terminated in up to 3 hours.