Having a bit of a chequered run here with 1Password...
I tried Wallet for the first time in Firefox (3.6.16), filling in Mastercard details. It inserted all data OK except for Expiry date. For some reason it came up with 07/2017 when it should have been 08/2012. Obviously I checked the wallet again and sure enough it does have 08/2012. The date in the form was a select field (not text) if that makes any difference.