I wonder if this is a tiny glitch or did the internal "ratings" of the people that voted change so for that reason the article grading is "fluctuating" in a non-obvious way.
Let me explain:
2 votes for 3,
2 votes for 4 and
16 votes for 5 gave an article rating of 4.33.
Later on the article get one more vote for 5 but no (to me) apparent change of the other grading. Then with the new 5-vote the rating went from 4.33 down to 4.28.
So a higher vote decreased the total rating? This I can understand if someones "reputation" point changed. Either a 5-voter got lower reputation or a 3-voter got higher reputation.
Either way to me it is unintuitive. Oh, and I did take some snapshots of this weird behaviour but I do not know how to upload them to this reply (if even possible)