If you open a CMakeLists.txt with QtCreator Beta2 and select your kits and configure the project, CMake is no longer run afterwards. And it looks like this:

You then either have to manually run CMake via Build -> Run CMake or close the project and open it again.

If you choose to run CMake manually, you can build the target that is selected at this moment (probably Debug). If you then switch to Release target, you cannot build, although it looks like you should be able to. Then you have to run CMake manually again to build Release.

If you want to reproduce this, just create the simplest CMakeLists.txt with a "add_executable(test main.cpp)" and a main.cpp with some simple main() function.