Once again: I'm quite sure, that rtw tix have to follow one general direction. Backtracking between continents is not allowed - it is only within one continent.
My experience is, that rtw rules are not well known to airline staff. So you may be just "lucky" if they booked it the way you wanted.
Trying to book LAX - GIG - LAX as a portion of my dec rtw was denied by LH rtw desk for that reason.