Magento 2 Why Credit memo reund tax from shipping cost?

Question

When create a Credit memo, I don't want to credit the Shipping cost, So in the field Refund Shipping, I just write 0. but system still refund the tax part of the shipping cost.

For example, if the shipping cost is 7 USD, and in the credit memo i write 0 in Refund shipping, the system will still refund 20% of the tax which is 1.4 USD.

Any ideas why this is happening?

Answer 1

This seems to be a bug in Magento 2.2.7 and is fixed in Magento 2.2.10. The error never appears when I upgraded the site to 2.2.10.