Thanks for the extra detail. We see a wide range of use cases here; what makes intuitive sense to some users seems undesirable to others. In some situations, the developer has to just pick something and stick with it.
I do see your point here though. If a new item after a Project does not inherit the Project prefix, it is reasonable to expect its prefix to be the default. That is what “default” means, after all – the one you use when there’s nothing else controlling the decision.
I expect someone will have a different perspective on this but I’m moving and renaming this as a Bug.
In the meantime, I suggest as a workaround that you get comfortable with the keyboard shortcuts to quickly change item prefixes. If you type a -
followed by a space at the beginning of a line it will change the prefix to Bullet. Or you can use the hotkey, which I think defaults to ctrl+shift+8.