miles earned query?

can someone explain why a 100% miles bonus is only 67%? is it because I flew on a discounted UC code?

01 Aug 2013 Gold Membership 100% Miles Flown Bonus in Disc Upper Class 3973 0
01 Aug 2013 Virgin Atlantic, ORD-LHR Discounted Upper Class 5930 5

[Neil]

It's because you're earning 150% of the actual flown miles on your UC ticket.

Only the lowest Y fares earn 100%, every other fare code/class earn more but your gold bonus is only on the actual miles flown.