Atom Generics (except A and Q) disappear from structure after saving in CML format

**Steps to reproduce**

1. Create any structure, for example, chain.
2. Click Periodic table.
3. Open Extended tab.
4. Click the "AH" button in the Atom Generics section, click the OK button and click any structure atom.
5. Click "Save as" button. Select CML format. Click OK.
6. Clear the canvas.
7. Open the structure saved at 5th step.

Expected result:
Atom Generics should stay at the structure after saving and display in the same way as before saving.

**Actual result**
The AH atom Generic disappears from the structure in spite of presence AH in the CML formula in the "Open" window.

FYI, A and Q stay at the structure after saving.
If at the structure there are a or Q and any other atom generics (that dissapeared when present at the structure alone), in this case the both atom generics stay at the structure after saving.
If at the structure there are several atom generics except A and Q, in this case all atom generics dsappears from the strcture after saving.

No file or test is named. Reproduce the issue with an AH atom generic, then trace the CML save and open paths and compare handling of AH with A and Q. Done means non-A/Q atom generics survive a CML round trip and display as before.

Written by the indexing model from the issue text.