World download in which the bug happens: https://www.dropbox.com/s/7lz28rra2ix5xm5/Endzerst%C3%B6rung.zip?dl=0
(There's already a redstone block drop for your convenience. )
If you put a redstone block into the spot of the sign that says "redstone block here", the command blocks do some stuff and then fill three blocks with redstone blocks, which each activates a row of 4 command blocks, the first of every row is a repeating command block. There is a scoreboard counter from 12 down 1 per execution and everything except the teleportation of one armorstand is dependent on the scoreboard being above 0. When the scoreboard reaches 1, it replaces the redstone block that powered it with a stone block. This is where the bug comes in: Even though the signal giving redstone block was replaced with a stone after less than a second, the armor stand still gets teleported, which means that the repeating command block still gives a signal through its chain.
Seems to be already reported in MC-89877, but there the mod "Mustek" marked it as duplicate of MC-7681. I don't know if MC-89877 is about the command still being executed or the comparator output staying on. The comparator thing works as intended (although it's annoying), but that the command still gets executed is a bug.