software defect on mixed currency splits

[cognitive.libertarian+ml at gmail.com]

I'm running into a problem when a split transaction involves both
mixed currencies, and like currencies.

Here's the scenario.  Rent is €500, and utilities is €50.  The bill is
paid on a USD-denominated credit card.  The credit card has a FX
commission cost to account for.  So here's what the transaction
*should* look like (assuming the realtime market FX rate is 1.28
EURUSD, for example):

[liabilities:credit card:usd] 

  rent  $640  --->  500 [expense:rent:eur]
  utils $ 64  --->   50 [expense:utils:eur]
  FX    $ 10  --->   10 [expense:banking:forex:usd]

  total USD debited: 714
  total EUR costs:   550

The above entry is impossible because of a software defect that forces
all transactions in the group to do a currency conversion, even when
the accounts at both ends are in the same currency (in this case, the
FX line item that does not involve euros).

So GC does this:

[liabilities:credit card:usd] 

  rent  $640  --->  500    [expense:rent:eur]
  utils $ 64  --->   50    [expense:utils:eur]
  FX    $ 10  --->    7.81 [expense:banking:forex:usd]

  total USD debited: 714
  total EUR costs:   557.81 <- false amount

This means the euro costs are 7.81 in excess of the actuals.  GC
actually forces an exchange rate to be entered on the FX cost, even
when both accounts involved are USD accounts.  

The workaround is to enter all the non-mixed currencies as separate
transactions from the group of splits.  It's messy, but seems like the
only option.