Debugging multiple apps in one CMake project

It should be possible to debug for example client/server software in one CMake project. The qtCreator project is configured with CMake and there are two or more sub-projects(sub-folders) which are executables. If you debug the client program, attach the server process via the debug menu, then the server can't be debugged(no error msg, breakpoints aren't noticed). This is not intuitively. Current solutions are: 1) Start client without debugging and attach server process to debugging(this way you can only debug one app) 2) Open two qtCreator windows and debug both apps