If the common part of the account names is shorter than the security symbol then the subtotal line will show the symbol. If not, the subtotal will show the security name.

If you have different security names for the same stock symbol, FN uses the first characters that each name has in common. If there are fewer characters in common than there are characters in the stock symbol, the system uses the stock symbol. There is no current option to always use the security symbol for subtotals, but this is a good suggestion.