Command blocks sometime don't check if a tag is true

Sometimes command blocks on a fast clock will not check if a condition is true every time. To replicate this, make a scoreboard objective called "example" and set its value to 1. Then put the command "tell @p[score_example=1] test" into a command block attached to a 20 hz clock. You will be spammed with messages. Then set your score in "example" to 0. The spam will not stop.