AR Credit Memo delete Line did not remove Tax amount

Hello,

Have you seen a similar case to the one depicted below and found the solution?

Or is this a standard functionality?

The issue can be reproduced at will with the following steps:
1. (R) Receivables
2. (N) Transactions > Transactions
3. Query an existing transaction (Invoice) or create one and complete it
   The Invoice has  the following lines:
   Line 1 ==> 100 GBP
   Line 2 ==> 50 GBP
   Tax
   For Line 1 ==> 20% ==> 20 GBP
   For Line 2 ==> 20% ==> 10 GBP

Total Lines + Tax = 180

4. select Action>Credit
5. Press (B) 'Credit Balance'
6. The amounts are correct and the standard message occurs :
APP-AR-11641: The balance amount of the transaction has been credited.
Please save your changes and complete the credit memo.