It may be so.
It appears that the account balances between USD and CAD only include transactions which have occurred after we turned on the multi currency. It does not register the CAD transactions from before that date and therefore it is confused when it sees a balance in the account as CAD but not in the data field where the multi currency balances data comes from.
It appears to treat these older pieces of data as undefined. Is this something out consultant should be able to try to find with Grid View pulling out the data or is it likely to be more complicated?
We would like to avoid the same issue if/when we turn on multi currency for another account such as AP.