"Use diagnostic flags from the build system" flag is not preserved in Diagnostic Configurations

"Use diagnostic flags from the build system" flag in Diagnostic Configuration is not preserved after QtCreator is restarted.

 Steps to reproduce:

1. Start QtCreator, open Options -> C++ -> Code Model tab.
2. Click in Diagnostic Configuration name.
3. Click Copy "Build-system warnings"... and enter a name for the new config.
4. In Clang Warnings, make sure that "Use diagnostic flags from the build system" is checked.
5. Click Ok, Apply, Ok to close Options.
6. Close QtCreator and start again.
7. Open Options -> C++ -> Code Model tab and click in Diagnostic Configuration name.
8. Now if your click on your custom diagnostic configuration, the flag "Use diagnostic flags from the build system" is unsed.

The same thing is happening in "Analyzer" Menu.

After investigation, I think the flag is not serialized in the file QtCreator.ini (see attachments). Note that this bug was already there in the Qt Creator 4.11.