How can I prevent Visual Studio 2008 from closing all open files when I open/close a solution?

I have a file, xyz.cs, open in Visual Studio 2008. If I open a solution, xyz.cs is closed, and VS opens up the files listed in the SUO for the solution.

I open another file (in this case a file not included in the solution, we'll call i开发者_如何学Pythont abc.cs). Then, I close the solution, at which point all open files (including abc.cs) are closed. In addition, xyz.cs remains closed. The only thing that remains open is my TFS source control explorer.

Is there a way I can prevent this automatic file closing behavior? Is there a reason this behavior exists that would provide incentive not to prevent this behavior?

Edit: note that no file checkouts are expected in this scenario.

The solution contains source control settings (amongst other things), so if you were to open (and edit) a file from outside of the context of a solution it would not be properly checked out, unless it already is checked out (and thereby is not readonly). To overcome your problem you can either create a solution that contains both the files (and projects) or open two instances of VS.