(Custom Worlds) Chunk Generation

This probably was put up already by some, but I was playing around with the Custom Worlds option, and I had Lava Ocean, Ocean raised to 100, and set Biome to Extreme Hills, and got some chunk generated pieces from what looks like a regular Ocean biome, with Ice because of the Extreme Hills as a more hilly form of Taiga, but they spawned in my world. Any reasons why this happened? Let me know, and thanks