Updating split transaction and its nested transaction will incorrectly update asset balance

[samfromlv]

1. Get an asset with balance 0
2. Add transaction with amount 100 to this asset
3. Observe that asset balance was correctly updated to -100
4. Split transaction into two parts amount 50 and amount 50
5. Observe that asset amount is still -100
6. Update transaction with amount 120 and both parts with amount 60, issuing 3 API update calls, one for parent transaction and one for each nested transaction

EXPECTED: Asset balance now is -120
ACTUAL: Asset balance now is -140. It seems every update will cause balance update, so parent transaction is updated from 100 to 120, so -20 is added, than each part is updated from 50 to 60, so -10 is added for both, so in total balance is updated to -40. This is incorrect.

Workaround: Update parent transaction first, then for nested transaction updates use skip_balance_update flag.