Odd mob "magnetised attraction" behaviour

Is this still a concern in the current Minecraft version 1.7.4 / Launcher version 1.3.8 or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

Is this still a concern in the current Minecraft version *14w11b / Launcher version 1.3.11 or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

Is this still a concern in the current Minecraft version 14w21b / Launcher version 1.4.4 or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

Still present in current 1.7.10

500-600 entities clearly shows the corner attraction behaviour. Hopefully 1.8's AI overhaul will resolve this.

it's modded minecraft

Oh good input @Mega linial X! Very well done! Yes the first two pictures show 'Rei's minimap' BACK IN v1.5, since then all the screenshots are vanilla minecraft!
What about the screenshots I uploaded for 1.7.10? It's very easy to build a bedrock holding cell then spawn hundreds of mobs and see what they do, so why don't you try it yourself on vanilla minecraft, and see if you can reproduce it too before posting such unhelpful and factually incorrect comments.

This might take a little explaining but I think I understand most of this behavior. You can repeat the merging behavior by placing a single block far above the ground and spawning multiple mobs on the block. If the position of any mob on that block is updated, they will all fly off at high speeds. This behavior might be caused by a similar stacking glitch/bug like tnt minecart explosions; the push back effect when two mobs collide will get multiplied, forcing the mobs away from each other at high speeds. As for the tendency of gravitating toward the edges, I will have to figure out how I will explain that.

I believe it relates to hitboxes glitching around, similar to the graphical glitches of mobs being seemingly pushed through the walls. They gravitate to corners because the game is still assuming that the holding cell is filled with the hitboxes of the mobs, meaning once they find themselves in those corners, it's impossible for them to move. This behavior is progressive, as you can see it happening with fewer mobs but becomes so extreme with higher quantities that you can no longer see the visual representations of the hitboxes that are causing the effect.
I just can't imagine how this glitch could be fixed, aside from forcing mobs to not stack on top of each other.

This can not be properly fixed if the number of mobs is large enough. Lets say you have about 100 mobs within a 1 block wide by 2 block long pen. Using normal blocks to build the pen, the mobs hitboxes seem to only go to the middle of a block. So the 100 mob hitboxes would have to fit into the 1 block long space. This combined with the push back effect of mob collisions would easily cause the hitboxes to overlap, and even share positions along the edges. It also doesn't help that the push back effect is multiplied when mobs stack. They get stuck on the edges because nothing is pushing them back towards the center to counteract the mobs pushing them outwards.

you are in creative mode so the creepers are not trying to chase you. so tey walk just randomly. if there is a wall the are trying to move forward but they cant bekause there is a wall if they are in a corner they will as long as they dont change the direcktion stay at the same place

Is this still an issue in the current Minecraft Snapshot 15w45b or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

Uploaded a new screenshot from 18w07c. Looks good to me. Please respond if you can still reproduce.