Spiders in a huge group insted of multiple spiders by spawner.

Spiders were in a huge group by a spawner, and when freeded they made more groups. It was like when you spawn tons of creepers in a 1x1 glass box they make a circle.

What I expected to happen was...:
Spiders would be all over.

What actually happened was...:
There was a giant group of spiders.

Steps to Reproduce:
1. N/A
2. N/A
3. N/A