I try to create a .h file:

• I hit Ctrl+N and choose "C++ header file".
• ext dialog requires file's name and location.
• I enter something like "MyHeaderFile.h"
• next dialog asks me if I want to add the file to the current project and to the SCM, and indicates that it will create file "myheaderfile.h".

Linux is a less stupid OS and supports mixed-case filenames. QtCreator should obey user's request and not mangle the filename uselessly (at least on Linux).