Renamed the "eid" field to "id" in the LineItemForm form, since the problem is found. It was the "id" property of the enclosing FormField. If we extract the form from FormField, we can still access the "id" field.

src/accounting/models.py

@@ -679,15 +679,6 @@ class JournalEntryLineItem(db.Model):
                             amount=format_amount(self.amount)))
         return getattr(self, "__str")
 
-    @property
-    def eid(self) -> int | None:
-        """Returns the line item ID.  This is the alternative name of the
-        ID field, to work with WTForms.
-
-        :return: The line item ID.
-        """
-        return self.id
-
     @property
     def account_code(self) -> str:
         """Returns the account code.