Here's the change list so far. This is important to pay attention to if you're making Zombie levels, as all changes (apart from one minor bugfix) relate exclusively to Zombie levels.
Note that many of these changes were also included in V1.27n-C, which was originally planned to be a full release, but in the end was only used for the first release of Doomsday Lemmings. Also, due to the improvements with the replay database, there will be an official update of every NeoLemmix-based pack I've made to use V1.28n.
* Some extra information is stored in replays, to facilitate use with the
Replay Database.
* Zombies can no longer press exit buttons, trigger a secret level trigger, or pick
up pickup skills.
* Zombies no longer count as "saved" when killed in a Karoshi level.
* Zombies are no longer included in the "lemmings out" counter.
* A level will now exit just as it would if all lemmings were dead / saved, if all
remaining lemmings are zombies.
* Zombies are no longer affected by the nuke.
* A sound is played when a locked exit is opened.
* Fixed the bug where replays couldn't be saved on postview text screens in the same
way they can on the regular postview screen or the "You found a secret level" screen.
* Fixed the bug where pre-placed zombie lemmings would be rendered as normal lemmings
on the preview screen (and in images saved from the preview screen).
* Fixed the bug where zombies would graphically revert to regular lemmings when using
a teleporter or dying in a triggered trap.
* Added an option to mostly use the old Zombie behaviour (from V1.27n-B and earlier). When
set, zombies will still count towards the goal in Karoshi levels, and they can activate
unlock buttons and pickup skills (but still not secret level triggers or exits). Also,
the level won't exit when only zombies remain if it's a Karoshi level. To activate this,
use the (Gim27) option.
* Added options for Rising Water, Clock Gimmick, Zombies and Old Zombies to the configuration
menu. These aren't very useful on their own though, as the level needs to be specifically
set up to use them.
Just to clarify on the second point (about Karoshi levels), a lemming becoming a zombie doesn't count as killing it either (just like falling out of the level doesn't).
And yes, zombies can still trigger any other object type, apart from exits, locked exits, unlock buttons, pickup skills or secret level triggers. So they can be used as trap bait (or perhaps teleporter bait) or made use of by directing them through radiation or slowfreeze.
If people were planning to make levels relying on functionality that's being removed, you can set the (Gim27) flag in the editor; this will revert most of the new changes to zombies, apart from the graphical fixes, the inability to trigger secret levels, and the level terminating when only zombies remain*.
* This behaviour will revert in Karoshi levels, but not in non-Karoshi ones.
