@Bigdaddie:
The number of scores in the average calc of your (Legend) tier is 400. That said, you will have experienced a floating average for quite a while. The fact that scores higher than your average result in ave. drops show that you have just passed that number. Any infamously high result from early times in the tier is now being kicked out and the average is stripped considerably.
@Zebouq:
First of all, don't think in +/- Par but absolute scores. They go into the calculation (9 hole scores doubled).
Second, if your average goes up you haven't yet played the neccessary no. of rounds in your tier. Don't worry about bad scores now - they will be pushed out in time, as BriRock described. When it comes close to tiering up, they will be long forgotten.
Concerning the lil ave. drops the explanation is not that easy. The amount of each change results from the difference between the new score and the one it kicked out - you have to know this one, too, if you wanna follow suit.
In the example above, 75 - 79 = -4 modify the calculation. Plus, as a Master the number of scores in the average is higher than as a TP. If one stroke difference counted 1/25 = 0.04 then, it's 1/40 = 0.025 now.