While debugging, if you make an edit and recompile, QtCreator fails to stop the application as it should do.  So you get a message that the linker has failed (because the executable is still running).  But then there is no way to stop the application.  The red box stop button is not there because QtCreator thinks it has already stopped the application.  The only way to stop the application is to exit QtCreator and start it again.  This behaviour is new in 10.0.0-beta 2.