"Fetch rate" button not doing anything?

[Mark]

Hello,

what is the "fetch rate" button in the multicurrency "transfer funds" 
dialog supposed to do?
Whenever I click it, nothing happens.

Even if the dialog is prepopulated with the exchange rate, then I 
overwrite the exchange rate with something else and then click the 
button, it does not switch the value back to what it was before...

Could not google it either...

Thanks,

Mark