I don't know why, but for some reason Cruel Flurry now only buffs the first 5 seconds of any single-target dot you apply, instead of the full duration. This is probably one of the reasons why no-one uses those anymore (it used to buff the next single-target dot over its full duration). I am pretty sure it is supposed to buff any single-target dot you apply within the next 5 seconds for its FULL DURATION.