The stem does not break if the plant is replaced as soon as it is broken.
To reproduce
Plant a big dripleaf and bonemeal it to create a stem.
At the same time as you break the top (Leaf) part of the plant place another. This can be achieved by pressing both left and right click at the same time.
It doesn't matter what block it is on, but the bug will only be visual if placed from a different angle from where the original was placed. (if you place the leaf facing north, doing the bug east, west, or south will produce the weird visuals).
Linked issues
is duplicated by 6
MC-215405
Dripleaf vines not connecting when replaced.
Resolved
MC-218751
breaking the top of a dripleaf doesnt break the stem or lower the leaf
Resolved
MC-219448
Big dripleaf can be placed wierdly on top of dripleaf stem
Resolved
MC-219900
Broken Big Dripleaf Stem
Resolved
MC-220182
1.17 Snapshot 21w11a - Big Dripleaf "Desync"
Resolved
1 more links
relates to 2
Attachments
Comments 5
Relates to MC-187569
Erik Broes
I would image this can be easily repoduced in the situation describe in MC-166437, but it is still probably a different issue causing this desync.
edit: tested and you can break the head without breaking the stem, but very different look.