For a comprehensive list of other examples of issues with item positions in the Creative inventory, click here.
All tickets associated with item placement in the Creative inventory are valid for cases introduced in 1.16 and later as per this comment. Exceptions exist, which are valid for their own reasons.
The bug
The spore blossom, despite being a flower, functions very differently from all other blocks called flowers. For example, most flowers are x-shaped and require a supporting block below, whereas spore blossoms are concave and require a supporting block above. Despite this, the spore blossom is placed right in the middle of a row of x-shaped traditional flowers in the Creative inventory.
How to reproduce
Open the Creative inventory
Locate Spore Blossom in Decoration Blocks
Locate Lily of the Valley in Decoration Blocks
Locate Cornflower in Decoration Blocks
Note that there is a considerable difference between these items
Can confirm. This may be intentional.