Marius D

Tested the latest snapshot yesterday and loaded the map of the server I play on with it. The map was generated in 1.6.2. My Witch farm did not spawn Witches anymore, confirming what Louis A. Nani said. Shall I open a new ticket for the specific bug that spawning areas themselves are not saved on old worlds? I do not want to start a new map on my server because our Witch farm and our Wither Skeleton farm doesn't work anymore.

Jago, I think what you contributed has nothing to do with the bug described here, but is instead a different one: Your screenshots show a world generation issue where a Witch Hut is partially "overwritten" by a small lake (those also generate underground sometimes), resulting in the Witch Hut being incomplete. The same can happen when for example an Abandoned Mineshaft intersects a Dungeon, deleting the Dungeons chests and / or part of the Mossy Cobblestone it consist of.
You should consider opening a new ticket for this bug.

I don't think this has anything to do with chunks and chunk borders.
Witches can only spawn in the 7 x 9 area of the hut itself (in the full height of the hut). As soon as any block in this 7 x 9 area is not within a swamp biome, Witches won't spawn on it, but any other normal hostile mobs will. The pictures I attached to this ticket show very well which parts of the Witch hut are unable to spawn Witches at all (red) and which will spawn Witches (green).

Confirmed. And yes, this is still a concern in the current Minecraft version, as you can see by my list of affected Snapshots, Pre-Releases and Full Releases. I kept track of this bug during the development of 1.5 and now 1.6(.1). I added almost every snapshot that came out once I saw that this bug still was not fixed. I'm starting to think this bug has very low priority for Mojang, regardless of this ticket having a very detailed description and being almost half a year old now.

That is true, but the ghost items visually go into the hopper without actually appearing in its inventory.
Can someone please open a new ticket for this bug? It's not related to MC-4 for sure, I just don't have enough information on what's causing this bug.

Another important observation I made:
If a structure like a Jungle Temple or a Desert Pyramid spawns close to a Swamp Biome, the part of it that intersects the Swamp can also spawn Witches.
My assumption, therefore, would be that the game simply goes by the rule: "If a structure (any naturally generated structure) is (partially) in a Swamp biome, Witches can spawn on the blocks the structure consist of."
Markku somewhat comfirmed this with what he said, see above.
So my suggestion for a fix of the bug we're discussing here would be to simply loosen up with the Witch spawning rules a bit, also like Markku said. Maybe make the game do something like: "If a structure is (partially) in a Swamp biome or a River biome, Witches can spawn on the blocks the structure consist of."
I checked a few seeds because that would mean if there's a River in a Jungle or Desert biome near a structure, you'd get Witches spawning in there, but the cases of that happening pretty rare, in case that's a concern.

I really hope this gets fixed for 1.5. 🙂

I don't think this is related to MC-4, but rather that it's a problem that only affect drops by Witches specifically.
On the server I play on, which is currently running 1.4.7, I can reproduce the bug in my Witch farm as well.
The method of killing the Witches doesn't matter, and what makes me think it's not related to MC-4 is the following:
Let's say a Witch drops, for example, 1 Stick, 1 Gunpowder and 1 Glowstone Dust. Sometimes, I can pick up only the Gunpowder and the Stick, but the Glowstone Dust turns out to be a ghost-item that I cannot pick up, eventhought it landed in the EXACT same spot as the Stick or the Gunpowder.
The Witch drops don't have to land on the edge of a block for this to happen. Therefore I think this is unrelated to MC-4.

edit: I can also fully duplicate what Olle Görling said.

Yeah, I tried my best to make sure what I describe is 100% correct, and I think I nailed the problem. Mojang sees every singly bug report, right? My hopes are that this is an easy fix and might be fixed in 1.5. 🙂