Return tax incorrect when returning part of order with promotion

Description

Step to reproduce

1. Configure a sales tax for item B. For example, 20%.
2. Create the discount reduction "Buy A, get B at 50%."
3. Check out an order that includes 3A + 3B items that satisfy the discount with the correct sales tax (e.g., sales tax for 3B is 300).
4. Complete the order.
5. Create a return for B or 2B.

Expected: Return tax is correctly calculated.
Actual: Return tax is incorrect (-100 for 1B and 100 for 2B). If you return all B items, the return tax is correct