A client has been running Odoo 9.0 for about a month now and we've managed to work out most of the issues caused by differences between OpenERP v7 (what they had been running previously) and Odoo v9, however there is one apparent bug in the POS module that caused transactions to fail.

If you try to put through an item with no value (i.e. $0), such as a free item, a no-sale, or accidentally tap the payment method twice, a red error box appears with the title "A transaction can't have a 0 amount. None".  Once this occurs, subsequent transactions queue up in offline mode and I have to manually save the data from the browser local storage, delete the local storage, then decode the data to re-enter it as a new transaction.  All of this is very tedious and we can't seem to solve it.  A transaction should be allowed to have a zero amount.  This is completely legitimate and the error should be handled better at very least.

I cannot find any discussion about this anywhere on the web.  Has anybody else encountered this?