Thought it was a result of playtesting in creative so switched to survival and was still able to mine bedrock (and jump out of the world for science!). This would probably go great with a mod that sends players to nether when they fall out of the world but with something more vanilla (mods wise) this is probably undesired behaviour.

To reproduce:
go to bedrock level. mine not bedrock itself but a block that can be that is next to it like stone. AOE mining will then destroy the bedrock.