In an old world, if you go above sky level, you can cross the barrier of invisible bedrock.
It started in 0.2.0 also known as demo version. If you fly or bild to sky level you can cross the old world invisible bedrock barrier!
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Added duplicates link: MCPE-261Player can fly out of the world and get lostCannot Reproduce
Resolution: Unresolved → Works As Intended

Works As Intended. See the comment by [Mojang] Aron Nieminen in
MCPE-261.