[finance] payment date refused when "check date not in the period" is checked

First configure the bank journal and check the option "Check Date not in the period".
Then create an invoice lets say in period 04/2011
Then create a new bank statement for period 05/2011 for example.
Import the just created invoice and set the dae in the period 05/2011
Then confirm the bank statement (after setting the opening and closing balance accordingly).
You'll get the error that the payment is not in the period.
If you untick the "Check date not in the period" option, the operation is accepted normally while the payment is indeed in the period 05/2011.

Version are those of release 6.0.2