Indeed - and it's best to do a mental calculation of what the extra Avios and cash would be by checking the difference between two full redemptions, one in CW, the other in WTP, to see roughly what to expect. It may be a small amount different due to the way that currency movements may have affected the originally calculated set of overseas taxes. Auto-pricing is also known to get it wrong too. In which case ask the agent to send the booking to the Fares department where a specialist can calculate it manually.