I downloaded and installed the new QtCreator 4.6 + Qt 5.9.4 with the online installer on Win10.
I opened the Cmake project I previously worked on with QtCreator 4.5. The project loaded and configured fine with QtCreator 4.6. But when the next day I opened the project in QtCreator, the cmake "Clean step" were empty ("No clean step") (in Projects menu). Moreover I could not restore it because in "Add clean step" combo menu only "Custom process step" were available.