Describe the bug
HetAtomTautomerv2 detects tautomerism at carboxylates. I'm pretty confident that this is a side-effect of allowing keto-enol tautomerism... But I do feel that carboxylates are a special case and should be excluded.

To Reproduce

from rdkit import Chem
from rdkit.Chem import rdMolHash

smi = 'O=C(O)CCC'
mol = Chem.MolFromSmiles(smi)
print(rdMolHash.MolHash(mol, rdMolHash.HashFunction.HetAtomTautomer))
print(rdMolHash.MolHash(mol, rdMolHash.HashFunction.HetAtomTautomerv2))

Expected behavior
I'd expect the neighboring carbon to be excluded from the carboxylate tautomeric region. I think the desired tautomerhash would be [CH3]-[CH2]-[C2]-[C](:[O]):[O]_1_0.

Screenshots

Configuration (please complete the following information):

• RDKit version: Fall 2025
• Are you using conda? no
• If you are using conda, which channel did you install the rdkit from?
• If you are not using conda: how did you install the RDKit? Schrödinger custom install

Additional context
I'm using this in the RegistrationHash. This causes a collapse of chiral carboxylic acids.