Azure ConnectionString using totally wrong login credentials - asp.net-mvc

Question

I have created an ASP.NET MVC website which accesses a database, both of which are hosted in azure. I have created a specific login and user to access the database and can see them in SSMS. I see the login screen for the website. The trouble is when I try to log in, the login fails telling me that the user cannot be found.
Here's where it starts getting strange. The login ID that cannot be found is not the login that I created or that which is in my web.config (or my app.config). Instead it is the master user that I have to access the db server and other areas of my azure resources.
Here is the section from the web.config on my PC that was used to publish to azure:
<connectionStrings>
<add name="CSSL" connectionString="Server=tcp:svrmysqlserver.database.windows.net,1433;Database=MyDatabase;User ID=sqlUser#svrmysqlserver;Password=q2wW£E;Encrypt=True;TrustServerCertificate=False;Connection Timeout=300;" providerName ="System.Data.SqlClient" />
</connectionStrings>
The Error message said
Login failed for user 'MasterUser'.
I added some debug code to get the connection strings that were available and being used on the server and tried again. I got the following:
Login failed for user 'MasterUser'.
ConfigurationManager[data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|aspnetdb.mdf;User Instance=true]
ConfigurationManager[]
ConfigurationManager[Data Source=tcp:svrmysqlserver.database.windows.net,1433;Initial Catalog=MyDatabase;User ID=MasterUser#svrmysqlserver;Password=MasterPassword;Connect Timeout=30;Encrypt=True;TrustServerCertificate=False]
ConfigurationManager[Data Source=tcp:svrmysqlserver.database.windows.net,1433;Initial Catalog=MyDatabase;User ID=MasterUser#svrmysqlserver;Password=MasterPassword;Connect Timeout=30;Encrypt=True;TrustServerCertificate=False]
Database[Data Source=tcp:svrmysqlserver.database.windows.net,1433;Initial Catalog=MyDatabase;User ID=MasterUser#svrmysqlserver;Password=MasterPassword;Connect Timeout=30;Encrypt=True;TrustServerCertificate=False]
I attach a code snippet in answer to the comment below - where did I get the output from? I added code in the handler to get the current values of the connection strings before returning. The function is on the data context and is the first attempt to read data from the database.
public ReturnInfo GetSystemRecord(out AppSystemRecord rec)
{
ReturnInfo ret = null;
rec = new AppSystemRecord();
//check that we have a hope of seeing this record - no records should have an ID of zero
try
{
var query = from x in SystemRecord select x; // ther should only ever be one
if (query.Count() == 0)
{
SetupAdminUser();
SystemRecord.Add(rec);
SaveChanges();
}
else
rec = query.FirstOrDefault();
ret = new ReturnInfo(); // defaults to all okay
if (rec.Status == SystemStatus.Created || rec.Status == SystemStatus.Updated)
SetupDefaultsForLookupTables();
rec.Status = SystemStatus.Normal;
SaveChanges();
}
catch (Exception e)
{
while (e.InnerException != null)
e = e.InnerException;
ret = new ReturnInfo(ErrorType.UnableToReadDomainObject, e.Message + "\r\n");
// THIS IS THE IMPORTANT BIT TO GET THE CONNECTION DATA
foreach (ConnectionStringSettings v in ConfigurationManager.ConnectionStrings)
{
ret.ErrorMessage += "ConfigurationManager[" + v.ConnectionString + "] " + "\r\n";
}
ret.ErrorMessage += "Database[" + Database.Connection.ConnectionString + "] " + "\r\n";
}
return ret;
}
I searched my solution for any uses of MasterUser in any file but found none, nor any references to the password, which was the correct MasterUser password.
I deleted both the website and database and started again to be sure there were no files lying around in the cloud but without any joy. Any ideas what is going on? Is there some sort of cache that I haven't invalidated? is there some rule whereby there must be a connection to the master?
Your help and ideas would be gratefully received.
Craig