Earning key fragments

Last week I earned all available chest for that week on Tuesday. Prior to earning all available chests, keys would drop randomly when I won a game, however after I earned all available chests, despite winning many games I did not get another key frag until the following Tuesday when another box became available to me. I earned that box the day it became available and am now looking at not getting another key frag for another week. It is my understanding that key fragments are supposed to drop randomly when you get a win regardless of whether you are eligible to earn a chest. If this is not the case then it needs to be changed. Because that would mean that you would get 4 key frags every four weeks and 4 chests every four weeks which would mean in 5 months you will have 20 of each. Once you use all of your keys you will have 14 chests and 2 keys left over(assuming every time a chest is available you earn it straight away and earn a key frag at the same time). Am I just unlucky and am not getting key drops for winning? Is this a bug? Or is this just how it is set up?