Gift Certs and Skip Shipping Address setting

Hi, I'm having number of problems with gift certificates, some of the problems have been posted before but so far as I can gather no one has been able to recreate the problem and as such fix it.

The problem is linked directly to the Product is virtual: free shipping option. Once set the cart insists that the customers selects a payment method despite the fact that they have already applied the amount payable from a redeemed gift certificate. in this instance the amount payable is £5 and the available balance on the GC is £50.

I've also noted that whilst the cart asks for a payment method only 2 of my 4 methods are actually shown; sagepay_form & money_order are shown where as dirbankusa & dirbankaus are not shown. When I add a physical product to my cart with the GC then all payment methods are shown but the cart still insists on one being selected.

And finely when I change the "Product is virtual" setting to No, Shipping Address Required everything works fine.

If anyone can offer any advice on where I should be looking it could be a great help.

Thanks
Tony