HELP! Case Insensitive Database On Case Sensitive Server

We need to install CI database on CS server, and there are some issues
with stored procedures.

Database works and have CI collation (Polish_CI_AS). Server has
coresponding CS collation (Polish_CS_AS). Most queries and procedures
works but some does not :-(

We have table Customer which contains field CustomerID.

Query "SELECT CUSTOMERID FROM CUSTOMER" works OK regardless of
character case (we have table Customer not CUSTOMER)

Following TSQL generate error message that must declare variable @id
(in lowercase)

DECLARE @ID INT (here @ID in uppercase)
SELECT @id=CustomerID FROM Customer WHERE .... (here @id in lowercase)

I know @ID is not equal to @id in CS, but database is CI and table
names Customer and CUSTOMER both works. This does not work for
variables.

I suppose it is tempdb collation problem (CS like a server collation
is). I tried a property "Identifier Case Sensitivity" for my
connection, but it is read only and have value 8 (Mixed) by default -
this is OK I think.

DO I MISS SOMETHING ????