Web sites will not share a custom membership provider

I would like two or more web sites to talk to the same database containing a shared custom membership, rolemanager and profile provider.
In the web configs of web sites in question I think I have followed all the recommendations ie
1) I have used <clear/> before adding the shared database with providers
2) I have used applicationName="/" when adding the providers
3) However, If create a user in one website, using the common database with providers, the user cannot login to the other website.  It can only login to the website on which it was created.
4) If I compare users created from different websites in say the aspnet_Membership table of the supposed common provider, the [ApplicationId] is identical for the users and matches that found in aspnet_Applications ie all are based on applicationName="/"
This manifests itself in the following circumstances:
A) I have a development machine with VS2008 and prod ...