Minecraft wiki entry for Development_versions, associated text: MC-5961 – Droppers and dispensers aren't triggered by 1 or 2 tick pulses.
MC-6047 – Comparator strings fail to transmit 1-tick pulses.
MC-7654 – Items disappearing of droppers in some situations.
MC-8022 – Furnace interface occasionally closes when adding fuel, deleting all items in the furnace.
MC-8597 – Named mobs don't have named babies.
MC-8790 – Scoreboard teams function does not accept @p or @r arguments.
MC-9685 – Comparators are still very inconsistent in 13w06a.
MC-9818 – Non translatable error message "Could not clear the inventory of <player>, no items to remove".
MC-10357 – Getting into a minecart with a mob in it crashes minecraft.
MC-10881 – Comparator coming off of chests, droppers, hoppers ... behave strangely.
MC-11044 – Adding items to brewing stand using dropper does not change state of comparator.