In my creative world I had broken the block that allows mobs to spawn in a biome island. when i look at my biome compass which leads me to that block, it still shows me that there is a biome there. I am not sure if i understand how the compass works, but if this is how it works then there may be a bug. This doesn't really cause anything bad in the mod, but i'm just telling you the bug anyways.

The compass works in an imaginary world of numbers and calculations, it doesn't use the block at all.