The new vines become useless when mined with a silk touch tool. Picking up a "silk touch" nether vine makes all the other vines of the same type in the inventory unplaceable–they can be "placed", but will not reduce the amount in the player's hand nor remain once logged out. The problem is worked around by picking up a non-silk touch vine.
Mods: Feel free to reword this if it doesn't make a lot of sense. I'll be on later to correct this.
Thank you for your report!
We're actually already tracking this issue at MCPE-65522, so I will resolve and link this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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