When you try to place another glow berries or weeping vines under the previous one, you'll find that you won't be able to do it. It's the same in both Creative and Survival mode.
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Duplicate of MC-279242.
MC-280066
You cannot place another Glow Berries/Weeping Wines under block of the same type
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As far as I'm aware, sweet berries have never been able to be stacked.