The chunk blending code replaces certain chunks of biomes with others. You'll get chunks of ocean or jungle inside of a mountains biome. Trees will also be cut off if they're on the border of this error.
MCPE-145750
Chunk blending error
Resolved
Works As Intended
0
As far as I know the blending is supposed to look this way, unless I don't understand your issue. Closing as WAI for now, if you're willing to elaborate more on why is this an issue, we'll discuss it and reopen.