The Bug
See the screenshot for an example. It took four vines to place – one for each block face. When using shears, only one vine is returned. You can lose vines by simply filling a block space with them, then using shears and repeating.
Expected behavior: one vine dropped per side covered
Actual behavior: exactly one vine dropped
How to reproduce
Place two blocks down, one block apart from each other
Place a block behind the gap and above it, see screenshot
Inside the hole, place a vine on each exposed side
In survival mode, attack the vines using shears
❌ notice that the vines block drops only one vine, despite having 4 within its block space
Linked issues
is duplicated by
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Attachments
Comments

I think you misunderstood this ticket. This is not a request for the ability to dupe vines by placing and breaking, this is indisputably a bug. You can lose tons of vines by simply placing and shearing. Also, is inconsistent that if there are multiple vines sharing blockspace and you shear them you only get one vine back regardless of how many vines you actually sheared at once.

Affects 1.13 as well as all of its snapshots and pre-releases.
Can confirm in 20w48a.

Inconsistency with Glow Lichen

Can confirm 1.17 release candidate 1

Can confirm in 1.17.1 Pre-release 3.

Can confirm in 21w44a.
Can confirm in 1.18.

Affects 1.18.1
Can confirm in 1.18.2.

I think @unknown doesn't understand how vines work. When you place vines, it places it on only one side of the block. So if you want vines on three sides, you must place three vines. Later, if you break the vines, even with shears, it drops only one vine, meaning two vines are lost.
People aren't asking to be able to place one vine and have it cover three sides then break it to get three vines back (meaning the amount of vines tripled). They are simply asking that if they place three, then break the three, they get all three back, instead of only one.
This is inconsistent with Glow Lichen and Skulk Veins.

@Jbomb01 Don't worry: the status of this issue has been updated since Grum's comment, and it is not marked as Working as Intended anymore. You can use the "All" tab to see his comment in the context of there changes that have happened to the issue, which should clear everything up.

Yeah I see that it is not Work As Intended anymore, but I wanted to make it clear what exactly was the bug, because if a Mojang employee didn't understand it, other people might not either.
Can confirm in 1.19.
Can confirm in 1.19.2.

Confirmed in 1.21.3
Placement feature doesn't mean you suddenly get more out of them 🙂