Are you comparing the total price on the final page, or just the indicative total price that displays on the page with the matrix of flights and WTP/CW/F?
The indicative price on the matrix page can be incorrect, especially when you select different outbound/inbound options. The fare split is only for indication, the total price on the payment page should match no matter how you originally searched when you've selected like for like fares.
Thanks, I didn't realise that.
I only looked at the initial prices displayed after the home page search, inbound and outbound (on same page). However, I hadn't selected different inbound/outbound - it was a basic IAD return.