I'm fully aware of Add and Replace behavior, and what they bring, as per what I wrote. https://medium.com/mobile-app-development-publication/7-common-mistakes-easily-made-with-android-fragment-6fc85c44e783.
However, in my case, we do have a page that need to prevent reloading (i.e. webview) for better user experience, while others are okay. Hence there need to be a mixture of them.
It is not as simple as using one or the other. If we have the option of doing so, sure, that would be an easy workaround.
Anyway, for the above bug, we do have workaround. It's just that we need Google to be aware of such possible strange issue, and trap that could puzzle many.