Fixed balance can be altered by editing old transaction

[ENargit]

Steps to reproduce:
1. Create new empty account
2. Add some income transaction, (i.e. 300 USD)
3. In the main menu click on the new account and choose 'Balance' option
4. Set some balance (i.e. 150 USD) // new transaction ( -150 USD ) will be added
5. Edit first income transaction and set income to 200 USD. (or add expence transaction with past time)
6. Observe current account balance

Expected result: 150 USD
Observed result 50 USD

When I use the 'Balance' option, I expect the value I entered to be consistent. For instance, I just counted money in my wallet or got information about my bank account status. And I know exact balance in this fixed moment of time. All inconsistences I put into a special category(i.e. Forgotten). If later I remembered some details about past transactions and changed them, I would like to have delta-value in the Forgotten transaction changed, and the balance kept.

I suggest to make a special type of transaction for balance setting.

Maybe this should have been an 'Improvement' blueprint instead of bug report, but for me this really seems like a bug.

Do you think it has to be fixed? I am Java programmer and can help with implementation.

CyanogenMod 7 (Android 2.3.7)
LG Optimus 2x