Mobs running in circles and not jumping when chasing/running away

I think you got the point so attachments won't be necessary.

Can't reproduce in 12w50a or 12w50b.

Is this vanilla minecraft or is it modded?

Vanilla, if it was modded i wouldn't put it here

I'll try to add more details

I've just noticed that they begin to spin when they are going to fall from a block ( going down on a mountain ) They begin to spin on the border of the block but don't go down to the next one ( that is only an only 1 block high fall ) and they don't jump either.

Confirmed.

Yeah, confirmed in 12w50b.All mobs sometimes do this(except ender dragon etc).

Confirmed. Happens in 12w50b. All you need to do to reproduce it is [edit:] just open the game an play it, it happens a lot.

confirmed, in other words: 12w50c

Confirmed. Affects (= tested on) at least chickens, sheep, zombies, skeletons and creepers, but not spiders (since they climb differently?). They can't climb or descend blocks, they just get stuck spinning on the edge. They also spin when they reach their destination on flat ground. Works correctly in 12w50a, so this broke in 12w50b.

Creepers, skeletons, sheep etc. except for spiders are all affected by this glitch.

Confirmed. It appears that mobs have forgotten how to jump up 1 block. Tested with cows, trying to lure them with grain: As long as I'm on the same level they follow me, but once I jump up on 1-block higher ground they go into spinning mode. Vanilla 12w50b.

As already noted, spiders are largely unaffected. Endermen also appear unaffected, as they do not jump, but also appear to always have their mouths open.

Iron golems and villagers do this too. Also the golems randomly swing their arms even though there are no monsters. (12w50b)

Can confirm. This seems to happen to all mobs with pathfinding. It does not effect Endermen and Spiders since they have no pathfinding.

It seems not dependant on jumping up or down blocks, mobs are spinning in flatland too: MC-4690

This happens in 1.4.5 too, I think it's when they became more 'fearless'. This isn't a new bug.

I can't confirm Nitrogen Snow's observations. In both 1.4.5 and 12w50a, mobs running in circles did happen but was just an occasional sight, nothing compared to what's happening in 12w50b. Also, mobs lured with their favorite food would follow you up and down hillsides without hesitation (just tested with 12w50a to be sure), while now in 12w50b they only follow you across a flat plain, and begin to rotate at the first 1-block jump. A new bug it is (and a show stopper if I'm asked).

I also can confirm that Iron Golems, Cows, Sheep, Pigs, Creepers, Skeletons, and Zombies all seem to randomly spin. As stated before, this was fairly rare in 1.4.5 and 12w50a, but has become very common in snapshot 12w50b. I can't say for sure about the other mobs, but I'm sure they are just as effected. BTW, I am on Mac OS 10.8.2.

actually it not just when they are trying to jump up a block. One skeleton in my world was in a desert biome out in the open just randomly spinning around.

I have observed this happening in 1.4.5 as well, though not nearly to this extent and usually AFTER going down a block, not before. My theory has been that their pathfinding is trying to take them along the small gap they 'skipped' from the forward momentum affecting their fall, thus doubling back, but have not yet tested this in depth. Looks like pathfinding was tightened up for some reason.

I've just noticed one thing, If you exit and then enter a saved world, mobs will be spinning no matter if they are trying or not to jump or fall a block ( superflat maps prove that ) But after that entering bug, the mobs will glich only on the current situations.( already written )

I have seen this with pigs, sheep, and chickens. Definitely confirmed.

not fixed in 1.4.6

still happens with chickens pigs. villagers(even when you didn't hurt them) and cows

I see pigs and cows spinning everywhere still. They seem more mobile than before, but it's not 100% fixed in 1.4.6

Reopening

@Maarten & Jacob: 1.4.6 won't be released until thursday; I presume you tested it with a pre-release (1.4.6pre).

I've just built a new sneaky version that fixes this for realz yo.

You'll have to redownload 1.4.6; it's not worth to do a .7 for a 2 character fix, so soon after publishing 1.4.6.

@christoph sight.. yes jacob. I thought that was kinda obvious

@Dinnerbone I get this when I click the download button on your site:
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<Code>AccessDenied</Code>
<Message>Access Denied</Message>
<RequestId>CBCFCD4B4DE0C3F4</RequestId>
<HostId>
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Confirm fixed with the "2nd edition" 1.4.6pre (animals still do make sudden quick turns on the spot, but no 360 degrees rotations).

Fixed in newly uploaded minecraft.jar please redownload here.

Not fixed! 1.8.7 still has it!

I didn't realize this was considered "fixed". I was about to make report when I found this one, mobs are still doing this for me. I am in 1.11.2. I even downloaded a fresh exe and expected this not to happen but it certainly did. Please look into this! It happens more so with mobs that have passengers because the AI doesn't take into account the size of the rootvehicle. A skeleton riding a horse for instance. The skeleton will try to go down a block with it's own AI (mob itself is only a block or less wide) instead of taking into account that the Horse it is riding is much wider and won't fall into a 1 block space.

Separate ticket, please.