Source: WowAce

I've attacked, killed and looted the Sha of Anger once this week, but have noticed upon consecutive kills on the same toon, that Rarity counts the new kills as a 'loot chance' and increases my percentage to get the Heavenly Onyx Cloud Serpent accordingly. Of course, seeing as how I can only technically loot the mount once a week, I believe this to be a bug.

Might be able to check loot lockout and bonus roll lockout quest. Potentially also applies to other situations (which ones)?

Actually, since the statistics are always used this would require counting the number of attempts done while already locked out, and then subtracting them from the total number of attempts (statistic + bonus rolls witnessed). Kind of messy, so not sure if I even want to touch this...