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
From a functional standpoint, wart blocks are to fungi what leaves are to trees. As a result, it would be expected they would come directly after leaves in Creative, however this does not happen.
Leaves should probably be moved to Building Blocks in the process.
How to reproduce
Open the Creative inventory
Locate Nether Wart Block in Building Blocks
Locate Warped Wart Block in Building Blocks
Locate leaves in Decoration Blocks
Note that these items do not even occur in the same tab
Can confirm in 20w48a.