I live (and pay my tax) in New Zealand, so my default currency is $NZ.
I have trading accounts in Australia and the US, so have portfolios for these set up in FM. When I use Transaction Retrieve (or QFX import) for an investment not already in FM, the currency for my new investment is always the default currency. This results in the amount debited from the cash account being wrong by the exchange rate factor.
The workaround is to change the currency of any "new" investment to that applying for the portfolio, delete the transaction entry and the corresponding cash account entry, and reload the transaction.
If there was a default currency setting for each portfolio it would get around this.