No mods, but it looks like it was loaded last in 1.15.2.
I'll make a new ticket if it doesn't already exist.
EDIT: Never mind. Found out later that I had loaded it in 1.15.2.
I encountered what looks like this bug yesterday in 1.16.2. Log attached.
This appears to be fixed in Minecraft 1.14 Pre-Release 3 (at least for me).
Not sure if this should count as a different issue, but I'm observing the same behavior on a world I just created in 1.13.2 when loading in 1.14-pre2.
UPDATE: I tested this again in 1.14-pre3 and it was not an issue.
I'm still seeing the bug myself in 1.14 Pre-Release 2. I tested with both a dedicated server and single-player world. I migrated from version 1.13.2.
This appears to be fixed with the new trading GUI.
Can confirm for 19w11b.
Still present in 14w34d from a world created in 1.7.10.
This should really be looked into before 1.8, as it affects worlds created in the current stable version.
When looking at a plant's data with F3, it seems that the plants that survive are the ones that are facing south. Those seem to get converted correctly--the rest don't and drop themselves.
Cacti, poppies, dandelions, and oak saplings in pots don't seem to exhibit this bug, but other plants do, such as ferns or spruce saplings.
The steps you tried before should reproduce the bug with ferns, for instance.
There don't seem to be any, but I attached the log.
I looked at an affected save file with an NBT editor, and it appears that the UUID was written to the OwnerUUID on the wolves without hyphens. Tamed wolves in newer worlds save the UUID with hyphens, and when I edited my old save to include hyphens, the wolves behaved normally.
This is not a duplicate of MC-39167. The problem here is not flower pots not dropping flowers when broken, but flower pots actually disappearing when loading a world. It seems to affect every plant except poppies, dandelions, cacti, and oak saplings.
I noticed that when you hit F3 and hover over the affected pots in 14w21b, "Round Trip Different" appears in the upper-right. I think this is a problem with the new block states.
I was aware of MC-153904, but that issue doesn't appear to have any log messages (other than some people getting "fetching addPacket for Removed Entity"). The log messages in my attachment are different, and more closely resemble those in MC-191501, which I had commented on before I realized I had last visited the village in 1.15.2.