This might be a bug in the new (managed) debug engine that ships with Visual Studio 2013. Try turning on Managed Compatibility Mode (which effectively turns it into pre-2013 debug engine), located under Tools – Options – Debugging:
If this solves the issue, then I’d suggest trying to reproduce it with a small project, and then reporting it on Connect, so it could be fixed.
@bjhuffine comments below that there are other ways to enable compatibility mode, without globally disabling it (e.g. per-project). More information here: https://devblogs.microsoft.com/devops/switching-to-managed-compatibility-mode-in-visual-studio-2013/