Conformer Generation Fails for three-coordinate Ns with specified stereo

[gncs]

Describe the bug
RDKit doesn't seem to be able to generate conformers for a three-membered ring with two nitrogen atoms if stereocenters are specified.

To Reproduce

from rdkit.Chem import AllChem

mol = AllChem.AddHs(AllChem.MolFromSmiles("N1NC1"))

c1 = AllChem.Mol(mol, quickCopy=False)
AllChem.AssignStereochemistry(c1, flagPossibleStereoCenters=False)

for isomer in AllChem.EnumerateStereoisomers(c1):
    AllChem.EmbedMolecule(isomer)
    assert isomer.GetNumConformers() == 1

c2 = AllChem.Mol(mol, quickCopy=False)
AllChem.AssignStereochemistry(c2, flagPossibleStereoCenters=True)  # flagPossibleStereoCenters

for isomer in AllChem.EnumerateStereoisomers(c2):
    AllChem.EmbedMolecule(isomer)
    assert isomer.GetNumConformers() == 1  # Fails

Configuration

• RDKit version: 2022.09.1, py38h5acb366_1, conda-forge
• OS: Ubuntu 20.04

[greglandrum]

Confirmed. Here's a simplified reproducible:

ps = AllChem.SmilesParserParams()
ps.removeHs = False
mol = AllChem.MolFromSmiles('[H][N@]1[N@@]([H])C1([H])[H]',ps)
AllChem.EmbedMolecule(mol)