I did not try to debug it. The point is that we have a working version, using make. Using the source files that you had (and I couldn't use your .sln file, because my version of Visual studio is older), I get the same problem that you and tabstop are seeing. So my conclusion is that YOUR FILES are broken (or something that is part of the build=step is broken).
I doubt that debugging inside the Bison code is the right way to solve the problem. Is part of your task to make this compile in Visual studio? If not, I wouldn't mess with the build process - just use the makefiles that already works, and get on with the ACTUAL task in hand [that is of course assuming you can reproduce the results that I got using the makefiles - there is a small possibility that the code only works with older versions of the compiler, but I'd really call that a slim chance, because I can reproduce the results of your project if I compile with the Visual Studio IDE].
Yes, I've been there and done that: You think you can fix some bit of code or build script by debugging - but I'm pretty sure that you'd be wasting your time if you haven't got a lot of time to work on this issue. Use what is working.
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Mats