Clang code model: many semantic issues after update to QtCreator 4.8 - 4.12/4.13

After update from 4.7 to 4.8, there are many unexpected semantic issues. Under 4.7, the clang code model plugin worked as expected. There seems to be confusion with symbols. 

I removed all history and installed a fresh instance of QtCreator (and the Qt 5.12). I also unchecked 'Ignore precompiled headers. These actions did not affect the behaviour.

Also changing the Diagnostic Configuration option does not have any effect on the behaviour.

Thank you.