[MC-115404] Items can duplicate if the item entity gets modified

The bug

A player in Survival or Adventure mode picking up and dropping items modified by the /entitydata command can duplicate the items.

How to reproduce

I made a quick little video, but I had to shove it on dropbox because of the 10MB limit

Link: https://www.dropbox.com/s/bqyjpazljppkirr/2017-04-04%2021-56-30.mp4?dl=0

Place a repeating command block, enter for example the following command (you can modify actual item entity tags as well) and activate it
```
/entitydata @e[type=item] {SomeCustomOrExistingTag:1b}
```
Place different variants of an item (for example different colored wool) in your hotbar
Switch to Survival or Adventure mode
```
/gamemode survival
```
Drop all items in your hotbar by either pressing Q or Ctrl + Q
Select the first hotbar slot and keep pressing Q or Ctrl + Q
→ After some time you should see that the dropped items have been duplicated

Linked issues

is duplicated by 2

MC-116788 Item duplication (advancement) Resolved

MC-117217 Items duplicate when stacking Resolved

relates to 1

MC-117217 Items duplicate when stacking Resolved

Attachments

entitydatacommand_itemduplication.mp4

Comments 17

tryashtar 2017-04-04T21:41:00Z

Looks like a duplicate of MC-114879, you were probably looking for something to do with /entitydata 😉

Nope. 2017-04-04T22:10:51Z

@tryashtar I just checked without entitydata, and this appears to be the case. How silly of me to not check for such a simple thing in the first place!

Nope. 2017-04-05T21:11:05Z

Please reopen. Although MC-114879 has been fixed, this STILL happens with entitydata.

CreepersPlayYT 2017-04-05T22:01:39Z

Nope. 2017-04-05T22:51:12Z

@CreepersPlayYT ???

7 more comments

Meri Diana 2017-04-10T08:09:33Z

(If you export such short videos without audio in 720p 30 FPS 8kbps, it should usually fit within the 10 MB limit 🙂)

Hello @unknown, I tested it, in one of my old test worlds as well as in a clean, fresh world, exactly like your setup, but it does not work for me? I tested in 14a and then also in 13b (the version you posted it in this bugpost), could you please test also in 14a if it still happens for you?

It simply doesn't happen for me, but please do tell if it happens for you still 🙂

Nope. 2017-04-10T09:25:47Z

@Meri Diana I have tested in thoroughly in 14a, and I am still experiencing the issue, but it happens much less often, and definitely only with /entitydata.

I'm not sure what causes it to not happen for you unless it is out of pure chance, although that is a possibility given that the issue is much rarer in 14a.

marcono1234 2017-04-10T09:42:13Z

Can confirm this for 17w14a, it looks like you have to be in Survival or Adventure mode

Nathan Adams 2017-04-28T09:54:04Z

Please let me know if this is still an issue, otherwise it was fixed some versions ago.

JUE13 2017-04-29T00:19:14Z

Still in 17w17b

Daggard M 2017-05-04T03:45:22Z

In the latest snapshot as well (17w18a)

Nope. 2017-05-13T15:48:00Z

Just updated the affected versions.

tryashtar 2017-05-13T16:50:26Z

I really can't reproduce this, after following your instructions for several hundred items. Can you really still get this to happen in 1.12 pre-2?

marcono1234 2017-05-14T14:14:58Z

It looks like you need to have different variants of the same item. I was able to reproduce this with only 2 same items as well but it happened less often there.

It appears the items duplicate when the player has just picked up the items (not even client-side yet?) and already drops them again.

Nope. 2017-05-14T15:14:14Z

@tryashtar I am able to reproduce the issue in both pre-releases, I used a fresh superflat world with default settings and I found that dropping a full hotbar resulted in multiple of those items being duplicated. Expanding on what Marcono said, I probably get successful results due to the fact I mostly test with multiple types of stone.

Nathan Adams 2017-05-16T09:21:01Z

After testing this out, I can reproduce it but don't need /entitydata (or any other commands) running. It seems that this is just MC-114879 and that we didn't fully fix MC-114879. I will reopen that and close this issue.

Nathan Adams 2017-05-16T09:35:49Z

Okay scratch my previous comment. MC-114879 is indeed actually fixed, but this is an edge case when the item entity was modified afterwards (such as /entitydata or a more simple case of "throw another item into the pile", as MC-117217).