This is not a bug, but rather a suggestion for an enhanced feature. Currently when you are working on transactions in foreign currency and a currency translation is needed the system always suggests the latest rate, which is maintained in the pricelist. This is doumented in the manual, thus the software behaves accordingly, but from a business poit of view something else is desirable.
Desired behaviour is that the system looks up the last rate (price) maintained prior to the posting date. This is rtaher handy in the situation when you are not working near time, but worj on two or three months of transactions in a row and have maintained the respective prices. My scenario for instance is this: I am still maintaining a FX account in the country where I am coming from, fund it every one-to-two month (the applied FX rate is the going rate for the next period coming), but post it actually in the system only eevry three, four months.

Reproducible: Always

Steps to Reproduce:
1. Maintain FX rates (prices for currencies) for April 1, 2013, May 2013 and June 1, 2013 for EUR/CAD. Home currency is CAD, while FX is EUR. 
2. Enter a transaction dated April 15, 2013 in EUR on a FX account and categorize it as an expense.
3. The FX popup is launched
Actual Results:  
The latest rate as of June 1,2013 is suggested.

Expected Results:  
The rate as of April 1, 2013 shall be suggested.

I am using version 4.61 on Ubuntu, but according to the release notes and the changelog it looks as if nothing has changed in the most recent versions (4.62 to 4.64) at that end.