Some traded volume updates ('trd') are sent due to changes in the underlying foreign currency exchange rates.
This is due to a trade involving two different currencies. Currency fluctuations may result in a new traded update being sent for a nominal amount, and can also result in a decrease in the initial reported traded amount.
You can monitor underlying currency update using the listCurrencyRates service. Please note: the currency rates are updated once every hour a few seconds after the hour (Monday-Friday) and are subject to the Forex market opening times.