1. Open a project.
2. Go to Projects mode.
3. Remove the "build-" from the build directory.
   This is needed to work around QTCREATORBUG-18150
4. Build the project using the 64-bit version of MSVC2015.
5. Close the project.
6. Remove the .pro.user file from the project's source directory.
7. Remove the kit you used for building.
8. Open the project again.
9. Go to "Tools" -> "Options..." -> "Build & Run" -> "Kits".
   A temporary kit was created that resembles the kit you used for building. It has a "Stop!" icon.
10. Select this kit.
    You'll see that the compilers don't match. The kit uses the 64-bit version for C and the 32-bit version for C++.
11. Go to "Compilers" tab.
    C and C++ compilers are available in 32- and 64-bit versions, so the kit could have used them.

An autodetected kit should be consistent and usable.