Creating a new monomer with an existing symbol overwrites the original

[ClairePA]

Steps
Create a new monomer and give it the same symbol as an existing one.
Save the monomer.
On saving the existing one is overwritten so it does not create a duplicate. (creating a duplicate would be bad). It would be better if it warned you first and refused to save at all.

[MarkusWeisser]

If the service gives an error, how can someone edit an existing monomer?

[ClairePA]

Current behaviour is that no monomers can be created at all.
Recheck once it is possible to create a new monomer.