When the user navigates to Tools -> Options -> C++ and perform following steps:

• Select the Code Model tab and then click the button for the current Diagnostic Configuration (which shows as being "Checks for questionable constructs").
• Then select an existing configuration such as "Checks for questionable constructs" and press the Copy button, followed by entering a name for the custom configuration
• Then settings the appropriate Clang Warnings flags before pressing OK to close the dialog and then OK on the QtCreator Options dialog.
• The custom configuration is present and works, I can go back into the options and see that my custom configuration is selected.

• As soon as I close QtCreator and relaunch it and go back into the Options for the C++ Code Model, the selected diagnostic configuration is "Checks for questionable constructs" again and my previously entered custom configuration is not listed any more as existing (there are no custom configurations at all!).