In a register, when entering txns involving foreign currencies, a problem arises

Suppose you begin entering a txn, and you remember you had made a similar one, so you use autocompletion, but then you realize that the 2nd account autocompletion presented is wrong, and you change the 2nd account to another.

Cases appear where autocompletion presents a txn whose currency is not the currency of your new txn. In these cases, the actual behaviour of gnucash leads to txn having a currency different from the currencies of its splits.

I consider that with autocompletion the txn currency shouldn't be determined until the txn is saved.