MoleculeModify[{"DeleteAtom", a}] behaving strangely

Question

I am encountering a strange error with the following molecule:

ClearAll[mol];
mol = Molecule[
    "C=c1[nH]nc(C(=O)N2CCN(C(=O)CCCOC)CC2)c1=CC=CC",
    IncludeHydrogens -> All
];

MoleculePlot[mol, {{27}, {28}}]

The orange hydrogen atom has the index 27, and the blue one the index 28.

Now I try to evaluate the following two expressions:

mol // MoleculeModify[{"DeleteAtom", 27}]
mol // MoleculeModify[{"DeleteAtom", 28}]

In the first case, I get back a molecule. But in the second case, I do not. I simply get back the unevaluated expression.

I wanted to see whether it was the bond with the nitrogen atom that was causing the problem. Evidently, it was not.

ClearAll[nh3];
nh3 = Molecule["ammonia", IncludeHydrogens -> All];
nh3 // MoleculeModify[{"DeleteAtom", 2}]

Question. Why does deleting atom 28 in mol not work? I could find nothing in the documentation of MoleculeModify to indicate that deleting that hydrogen should not work.

EDIT

Mathematica Version 13.0.1, Windows 11 Pro

Answer 1

This bug was fixed in version 13.1:

In[1]:= mol = Molecule["C=c1[nH]nc(C(=O)N2CCN(C(=O)CCCOC)CC2)c1=CC=CC"];                                      

In[2]:= mol // MoleculeModify[{"DeleteAtom", 27}]                                                             

Out[2]= Molecule[<C18H25N4O3>]

In[3]:= mol // MoleculeModify[{"DeleteAtom", 28}]                                                             

Out[3]= Molecule[<C18H25N4O3>]

In[4]:= $Version                                                                                              

Out[4]= 13.1.0 for Mac OS X x86 (64-bit) (June 16, 2022)