membership provider not work well in Turkish (maybe also another non-English) culture

Hi everybody;
The membership provider uses ToUpperInvarint() (I guess) function for upper casing the userName, and it fails to found users have a culture specific letters, so not work well and throw exception.
for example: in Turkish culture, the upper case for "admin" is "ADMIN" with toUpper() method and is "ADMIN" with ToUpperInvariant() method. because the membership provider uses ToUpperInvariant for userName and UPPER([userName]) in its SQL query it fails to found some users. (my sqlserver installations is also in uses Turkish culture for default)

My SQL Server Database Collation is: Turkish_CI_AS 
I don't know how to fix it, please guide me? thank you