I am able to reproduce the problem and found a workaround that seems to solve it.
After you create your .resx file, right click it and choose properties, then change Custom Tool from GlobalResourcesProxyGenerator to PublicResXFileCodeGenerator
then you can reference it with
using acme.Web.UI.App_GlobalResources;
and code like this now works:
btnSubmit.Text = GuestBookResources.SubmitButton;
Hope it helps,
Joe