Project Settings Environment doesn't take place right after adding the variable

I added essential environment variable via Project Settings to fix the project's CMake configuration, but it doesn't get applied right after adding.

I can see it added in System Environment of Build configuration (in my case it's PKG_CONFIG_PATH variable), but the projects still fails to configure.

Workaround:
If I Unset the variable with the button, and then Reset it immediately, the variable gets applied and the project configures then successfully.