entities in 1x1x2 area mass escape when too many

I am playing the 1.1 release of MCW10E My chicken farm needed some tuning up so i cut off the Egg output and routed it to a collection bin ~6 shulker boxes and a few hoppers.

When i hooked everything back up to my automation to pile the chicks into a 1x1x2 area (made of glass with hopper on the bottom and a bottom slab on the hopper), it looked very silly. Everything was hooked up to a redstone delay to lava the chickens every 30 seconds.

Well when so many of the chickens grew up, they exploded out of their tiny pen (not the creeper kind of explosion) it was like chicken fireworks but not blowing up. i lured them into a 2x2x2 hole in order to contain the issue. I will be uploading and leaving a link to the video i was able to capture.

To duplicate, create an auto-firing dispenser using a comparator to detect items in the dispenser with a repeater running into the dispenser to fire it any time there is an item. Then add a few hoppers running into that dispenser with 3 double chests full of eggs. Fire the eggs horizontally into a water elevator so any hatched eggs will swim up, Use the same water physics to conveyor-belt the chicks to a 1x1x2 holding cell where they will land on a bottom half slab. Do not kill any chickens as they need to grow into adult chickens for this to work.

for extra measure, add another cell close by with adult chickens. This is what i believe helped the explosion. many baby chickens wanting to go toward the adult ones cause them to bunch up in a corner.

I have duplicated this 4 times so far, so don't try and tell me it is not a thing. I have a video link coming soon (it's uploading now)

(EDIT) Here is a link to the video.
https://youtu.be/U8OA3dcbrOc
the explosion occurs at 14:30-14:35

Tutorial on how to duplicate is coming soon. I can do this reliably. Will be doing similar where i capture this happening. i will try to keep count of the chickens that go in to see if this could be a numbers issue. Stay tuned.

Mod Note by @unknown:
When the chicks start to grow into adults, the others start to get pushed out forcibly.
(Highlighted this point above.)