Create a new project. Use Kit Build settings of: "Debug" and "Release" for the Build directories/.
On Linux and MacOSX this will properly build the symbols and output targets into the appropriate folder such as "Debug" or "Release" folder in case of shadow builds as original specified.
However opening the same project and running QT Creator on Windows it creates an even additional debug and release folder in both the original Debug and Release folders.
If you also disable shadow builds on Windows, it STILL creates a debug and release folder in the project folder.
This is very annoying when you are building a cross-platform library and then trying to use that library from an application.