How to edit a split transaction in gnucash

Question

I have a split transaction in gnucash which transfers 10.40€ from my Checking Account (split line 3) to my Expenses:$ account (split line 1) as 20.80$ via Trading accounts: (I know 1€ is not worth 2.02$ (at least as of 2018-04-06) - it's just an example)

As seen from the "Expenses:$":

                      account   | Tot expense | Tot Rebate
--------------------------------+-------------+------------
                     Expenses:$ |     20.80 $ |
           Trading:CURRENCY:EUR |     10.40 € |
Current Assets:Checking Account |             | 10.40 €
           Trading:CURRENCY:USD |             | 20.80 $

Basically, I pay an expense in USD from my bank account in EUR.

Now, I want to edit this transaction, because at the moment my bank followed through with the transaction 20.80$ are only worth 10.00 € (instead of 10.40€), so I edit 10.40 to 10.00 twice

                      account   | Tot expense | Tot Rebate
--------------------------------+-------------+------------
                     Expenses:$ |     20.80 $ |
           Trading:CURRENCY:EUR |     10.00 € |
Current Assets:Checking Account |             | 10.00 €
           Trading:CURRENCY:USD |             | 20.80 $

Then I hit tab until the end of the transaction; A "Save the changed transaction?" dialog pops up, on which I click "Record Changes"

Expected result:

                      account   | Tot expense | Tot Rebate
--------------------------------+-------------+------------
                     Expenses:$ |     20.80 $ |
           Trading:CURRENCY:EUR |     10.00 € |
Current Assets:Checking Account |             | 10.00 €
           Trading:CURRENCY:USD |             | 20.80 $

Actual result:

                      account   | Tot expense | Tot Rebate
--------------------------------+-------------+------------
                     Expenses:$ |     20.80 $ |
           Trading:CURRENCY:EUR |     10.40 € |
Current Assets:Checking Account |             | 10.00 €
           Trading:CURRENCY:USD |             | 20.80 $
                  Imbalance-EUR |             |  0.40 €

• Why does gnucash only apply half of my edit? (Introducing the imbalance account for unbalanced transactions makes somewhat sense for me)
• How can I achieve my expected result without starting the transaction from scratch?

---

Edit 1: Editing the actual result doesn't work like I expected either:

First, I edit the Trading:CURRENCY:EUR expense from 10.40 to 10.00 and remove the Imbalance-EUR account line from the split.

                      account   | Tot expense | Tot Rebate
--------------------------------+-------------+------------
                     Expenses:$ |     20.80 $ |
           Trading:CURRENCY:EUR |     10.00 € |
Current Assets:Checking Account |             | 10.00 €
           Trading:CURRENCY:USD |             | 20.80 $

Then I hit tab again until the safe dialog appears, on which I click "Record Changes".

Expected result:

                      account   | Tot expense | Tot Rebate
--------------------------------+-------------+------------
                     Expenses:$ |     20.80 $ |
           Trading:CURRENCY:EUR |     10.00 € |
Current Assets:Checking Account |             | 10.00 €
           Trading:CURRENCY:USD |             | 20.80 $

Actual Result:

                      account   | Tot expense | Tot Rebate
--------------------------------+-------------+------------
                     Expenses:$ |     20.80 $ |
           Trading:CURRENCY:EUR |     10.40 € |
Current Assets:Checking Account |             | 10.00 €
           Trading:CURRENCY:USD |             | 20.80 $
                  Imbalance-EUR |             |  0.40 €

• Why does this edit not change anything?

---

I'm using Windows 10 and GnuCash 2.6.19.

Answer 1

Basically, I pay an expense in USD from my bank account in EUR.

If this is the only thing you are trying to do you should not require the split transaction and currency trading accounts.

When expense transaction in foreign currency is saved the dialog pops up that asks to specify an exchange rate. This is documented in "12.4. Recording Purchases in a Foreign Currency"