Hi
I am planning a RTW ticket and not sure if the following is a bug in the system or in my understanding. The following prices without issue
OSL-HEL-DFW-EZE-JFK-HND-SIN-HKG-AKL-NAN-MEL-BKK-LGW - (surface) -LHR-LCA-LHR-OSL = 16 segments (bold = stopover)
However attempting to swap the BKK-LGW + surface = 2 segments to BKK-HEL-LHR = 2 segments brings up the
"Your itinerary exceeds the 34,000 mile limit on a Business or First class booking. To finalise your itinerary, please reduce the length of your trip." error
From what I can see both options should be equivalent from a segment point of view and the routing via HEL is not adding any stopover.
Can anyone see an issue or is this a bug?

Edit:
Interestingly I just tried some other BKK-LHR options and swapping to BKK-KUL-LHR will price as will BKK-HKG-LHR and BKK-CMB-LHR but via DOH, MCT or HEL error