A quick tip that may save a lot of anguish.
The UML diagrams and editor in Visual Studio 2010 Ultimate are excellent, and you can quickly and easily create very snazzy diagrams like this:
– and link components to TFS Work Items.
But if you want to base a new diagram from an existing one, don’t copy and paste the file from Solution Explorer. VS will let you do it, but what you end up with is effectively a shallow copy, where components in your new diagram are using the same element IDs as the old diagram, so if you make a change in one, it will be duplicated in the other.
VS will give you a hint with this warning if you try to open both files:
“Cannot load ‘x.y.z.sequencediagram’: Element with ID [guid] already exists in element directory”.
Instead, create a new file and copy-and-paste all the elements from the old one, and they will be created as new elements in the new diagram.