Charlestown was not part of Boston until 1873. Before that it should be just Charlestown, Suffolk, Massachusetts, United States, not Charlestown, Boston, Suffolk....
According to Wikipedia, "Charlestown became a city in 1848 and was annexed by Boston on January 5, 1874. With that, it also switched from Middlesex County, to which it had belonged since 1643, to Suffolk County.
If you take a look at the Places Database for Charlestown at: https://www.familysearch.org/research/places/?focusedId=10686226&searchTypeaheadInputText=Charlestown,%20Suffolk&text=Charlestown,%20Suffolk you will see the four historical time periods that have been entered for it and that the database correctly shows Charlestown, Middlesex, Massachusetts, United States for 1776 to 1874. This is the standardized version that is available in Family Tree:
@Helen Schatvet Ullmann is calling out some cruft in the standard place name database (gazetteer). The Boston area has a bunch of standard names that are not quite right.
Helen, the site Gordon linked has a process where you can enter feedback about individual standards that need improvement or removal because they are duplicates or for other reasons.