I've been playing in all of the snapshots and I've been using dispensers to spit out command blocks (setup is shown in the picture). When the command block is powered by the redstone block, it triggers and turns on the comparator because it successfully executed the command. However, in 14w27b, it doesn't output the signal via comparator even though it did work in all other snapshots that I've played on. (The commands in the dispenser just change a scoreboard value, I thought I should add that in case it matters). If I remove the redstone block and place it again, it updates and outputs a signal through the comparator.