If you place (using /setblock) a half (upper) of a tall flower in the air and switch to survival mode and you break it, you don't get anything for it.
MC-169235
Halved upper tall flowers don't drop anything when broken
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1
(Unassigned)
Confirmed
(Unassigned)
1.15.1, 1.15.2 Pre-Release 1, 1.15.2 Pre-release 2, 1.15.2, 20w06a, ..., 1.16.5, 21w11a, 1.17.1, 1.18.2, 1.21
Retrieved
Only the upper sunflower doesn't drop a flower when broken. (1.16.3)