There's no warning when you're about to open worlds from old versions

I believe this affects worlds from all previous versions, including older releases, snapshots, and pre-releases.

Ordinarily the game would warn you when you try to open an old world in a new version and ask if you're sure you want to update, but it doesn't. There's no exclamation point next to the play button, nor is there a screen to confirm your choice to update.