Update a primary key value using SubSonic 2.2

I'm currently developing an app using SubSonic 2.2 and I'm having problems updating one of the columns of a composite PK on a table.

My code is roughly this:

foreach (pageItem page in pages) {
    page.IdFile = newIdFile;
    page.PageNumber = counter;
    counter++;
    page.Save();
}

This does not update my record.

My pageItem table contains 4 columns that make up the PK. I only need to update one of them to simulate that I'm moving a page object from one file to another, to avoid creating a new record just to copy essentially all the same values except for that Id and the page number.

When I use SQL Server profiler then I can see that the following code is emitted to the DB:

exec sp_executesql N'UPDATE [dbo].[pageItem] SET [IdFile] = @IdFile, [PageNumber] = @PageNumber WHERE [IdPage] = @IdPage AND [IdCont] 
= @IdCont AND [IdExp] = @IdExp AND [IdFile] = @IdFile; 
SELECT @IdPage AS id',N'@PageNumber int,@IdPage int,@IdCont int,
@IdExp varchar(1),@IdFile int', @PageNumber=4,@IdPage=329, @IdCont=1, @IdExp='1', @IdFile=156

So basically my problem is that the update is NOT using different values for the old and new IdFile keys, they're both using the @IdFile parameter.

Is there a workaround that would preferably not involve using CodingHorror for example, that I may use to update my records? I don't mind using a raw SQL statement, it's just that I'm very interested in using SubSonic to its full potential, so any advices will be greatly appreciated.

Regards,

Fernando