Authentication type is changed itself, why?

Hello,

We have power BI report server on-premise. In Data Source > Authentication Type settings, our reports are set as Basic Authentication. But if someone opens report in power bi desktop, changes somehing then saves and closes.. reports Authentication Type is turning to Windows Authentication. Is this a bug? We cant't access reports in windows authentication so we want to edit reports but we don't want to change authentication type. How can I prevent this?