Visual Studio 2012 does not show folder has been created

The Visual Studio project does not parallel you filesystem. If you create a directory or add a file into a directory through Windows Explorer, it will not show up in Visual Studio. You must either create the file or folder inside Visual Studio or use the Add... dialog for the project to add existing files.

The simplest solution for me was to recopy the files/directories from the project folder and repaste them on the Visual Studio Solution Explorer panel.

That's it!

Visual Studio will automatically sync file explorer with the Visual Studio file system.

Yes, this is because Visual Studio needs all its resources explicitly listed in its project files. When you add a folder in VS, it creates it on disk and changes the project file - whereas if you've added it in Explorer, the project file won't have any information about it.

The simplest solution I find is usually to rename them in explorer, add them in Visual Studio, then move the content from the original folder into the new one.

Alternatively, you could edit the project files directly, but that's slightly more advanced and dangerous. (It's not really that hard, and probably worth experimenting with if you've committed the "known good" project file.)