Why does updating a web reference in a web application require the project file to be checked out?

From: Declan (anonymous_at_discussions.microsoft.com)
Date: 03/22/04 

Date: Mon, 22 Mar 2004 11:36:10 -0800

I am using .NET 2003 in conjunction with SourceSafe 6 to develop web applications. Why does updating a web reference in a web application project require the project file to be checked out? This is very inconvenient if you have several developers working on a project, many of which need to update various web references continously?