Default membership provider username length

So i am maintaining a legacy application that requires the use of default membership provider

System.Web.Providers.DefaultMembershipProvider, System.Web.Providers, Version=2.0.0.0 etc etc

I've been tasked with implementing ability to allow user to have his email as their username....i've adjusted the underlying "User" table so that the new username field length is an nvarchar(256) not null but i get entity validation errors when i create a user with a username larger than 50 characters.  all is well under and up to 50.

Does the membership provider have a hard coded limit on username length? if so can it be easily adjusted?  I'd hate to have to write a whole membership provider when the only thing that i require is a longer username.

Anyone done this before?  Possible without writing your own provider?