Visual Studio Build Error: Could not copy the file because it was not found

Recently we got a bunch of errors when building a project in Visual Studio 2013, complaining about missing content files:

Could not copy the file "C:\projects\OurProject\images\image1.png" because it was not found.

We checked the files in the file system, but they have really disappeared. We had luck, as we had the original files under source control, so we could restore them from the repository. But it did not provide a long-term solution, as we got the very same error on the next build, so we had to restore them again. Restarting Visual Studio did not help as well.

To prohibit further deletion I set the files as read-only. It led me to the solution, as we got this time another build error message:

Unable to copy file "C:\projects\OurProject\images\image1.png" to ".\image1.png". Access to the path ‘.\image1.png’ is denied.

The problem was that the Output path (under project properties Build / Output) was accidentally deleted, so Visual Studio was to create the build at the source file location. Resetting the original value, the default bin/debug path resolved our issue.

One can simple reproduce the issue, simply create a new project (let it be a Console Application, for example), add an image as content file (Build Action = Content) to it and set its Copy to Output Directory property to Copy always. Then delete the content of the Output path property, save the project and try to build.

I know that it was our mistake, but to tell the truth, I would expect Visual Studio not to delete my source files, but rather validate my input, and not allow to leave the Output path empty.