How can I stop Visual Studio removing Office files from the solution automatically?

I've been developing a project for a while, and we have started a "documentation" folder 开发者_运维技巧 in the Visual Studio 2008 solution so that we can keep the developer documentation (and a few other useful files) in there (it's one of Visual Studio's solution folders, rather than a project). We're also using the AnkhSVN plugin so these files get copied to Subversion.

However, every time I save any of the files, Visual Studio automatically removes it from the solution, so I have to add it back in,and then close Word again without saving.

I'd have thought this was a fairly easy problem to solve, but the past three weeks (and reading many spurious results on Google for almost every search query I can think of that might be relevant) seem to have proved me wrong.

Does anyone have any ideas how to stop this behaviour?

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I don't know if this still happens with VS2013, but for VS2010 here is a detailed explanation on the cause and a work-around:

• Word files disappear from "Solution Items" in VS2010

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Are you sure the files are removed and not just hidden? I had a similar thing with non-code files.

• Showing and Hiding Hidden Files in Visual Studio 2008