When using block.setBiome() or World.setBiome(x, y, z, biome) the blocks that are updated are far more than the expected 4x4 area based on the location specified.

I used the same code and JAR as in the cloned bug:

Block block = event.getClickedBlock();
Location loc = block.getLocation(); 
loc.setY(0); // Set Y to 0 so it appears/updates in-game
loc.getBlock().setBiome(Biome.JUNGLE);

I clicked the block and a large area of the chunk changes biome. For example, when clicking the gold block in the attached image, the biome changes for every dirt block shown. This was from just one setBiome call on the gold block.

The attached plugin is the same as the cloned Jira - if you right-click the ground with a stick it will change the biome to Jungle.

Is it vanilla operation now that the biome is indeterminate or randomized?