Sourcesafe checks out Control files, but makes no changes

I have a problem using Sourcesafe in VS2008.

When I open certain controls in VS2008, I get an odd sequence of events;

• The files are checked out of sourcesafe (MyControl.cs, MyControl.designer.cs开发者_运维问答, and MyControl.resx)
• Visual Studio displays a dirty flag for the file (* after the filename)
• When I save the changes and diff the files, I cannot detect any changes.

Does anyone have an idea why VS might be making this 'null change' to my file, and how I might be able to stop it doing so?

Thanks for any ideas.

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I have been thinking about this off and on for a bit and I was wondering if it could be something to do with font scaling? If someone using the form has large fonts turned on then that might alter it in a subtle and non-obvious way.