Zork Zero

1. In version 296, you can't PUT things IN GONDOLA.
2. In versions 296 and 366, when you're sitting, GET ON MY FEET works, but STAND ON MY FEET says it's useless.
3. In versions 296 through 383, in the presence of the dirigible you can THROW HANDS FROM GONDOLA. You get, "You fling your hands out of the gondola."
4. In all versions, DRINK FROM LAKE causes a crash. The Infocom interpreter produces some odd visual effects, but Frotz exits with "Fatal error: Stack overflow".
5. In all versions, if you PUT HAND THROUGH DOOR or PORTCULLIS, you get, "You missed.", and your hand falls to the floor. If you PUT HAND THROUGH WINDOW or MURDER HOLE, your hand falls to the outside location below. It doesn't show in the description, but from then on you can only interact with your hand in that location.
6. In all versions, you can end up at Underwater without drowning. Leave the pigeon on the chessboard, pick up the perch with the waldo, start descending in the bathsyphere, wear the cloak, then get the pigeon. This teleports the player to Underwater, but outside the bathysphere. The sphere disappears after a bit. Objects can be picked up and dropped in this room, and they do not sink, despite the fact that if you are inside the bathysphere and drop an object from the waldo in the room Underwater, the object sinks to Lake Bottom. The jester can even appear in Underwater, you can send a chess piece there, and you can even be eaten by a grue there. If you are standing in Underwater and try to open the bathysphere to re-enter it, the game responds as if you opened the sphere while you were still inside it--immediate drowning. --Marco Cavagna
7. In all versions, if you EMPTY, READ, or WEAR something you're not carrying, ZAP something WITH it, or AIM it AT something, you pick it up. You can use these to pick up the ceramic pigeon without teleporting.
8. In all versions, the fish tank is closable. You can PUT objects IN the closed fish tank, but you can't see or interact with them.
9. In all versions, once you have opened the small louvered door containing the Tower of Bozbar, you can PUT things IN SOUTH DOOR, even though you're told it's closed. Anything you PUT there is no longer visible, but you can GET it FROM SOUTH DOOR.
10. In all versions, if the candle is lit, then LIGHT CANDLE says, "It already is!", but BURN CANDLE says, "[with the candle] You relight the candle."
11. In all versions, you can WEAR the ring of ineptitude when you're already wearing it.
12. In all versions, you can CONSULT anything ABOUT anything. You get, "You begin flipping the pages... You can't read about things in [object]." If you READ ABOUT something outside the library you get, "You begin flipping through the pages... There's no encyclopedia here to look it up in."
13. In all versions, if you REACH IN an open container such as BAG or CRATE, you get, "There's nothing in the [container].", true or not.
14. All versions have a parser bug that can show up if you're carrying more than one key. Here's how it works:

     >OPEN DOOR
     The door is locked.
    
     >UNLOCK IT
     [What do you want to unlock it with?]
    
     >IRON KEY
     [In other words: unlock it with iron key]
     ["it" meaning it]
     ["it" meaning it]
     But it isn't locked.
    

    Note that UNLOCK IT WITH IRON KEY would have worked just fine.
15. In all versions, at Hothouse, JUMP OUT WINDOW says, "You cut yourself to ribbons on the broken glass.", but nothing happens to you.
16. In all versions, if you WEAR the ring of ineptitude at Ledge in Bottomless Pit or Mouth of Cave, you get, "As you slip the ring onto your finger, you clumsily lose your grip, and plunge downward. Wasn't that fun?" The last sentence happens because the game tries to kill you by making you jump. --Marco Cavagna
17. In all versions, if you are carrying the rooster and either the worm or fox, and you go to the chessboard plain, FrobozzCo Offices (above Floor 2), or Construction area, the one eats the other, even though you're there. --Marco Cavagna
18. In all versions, at Gaming Room, OUT takes you directly to West Wing, bypassing Peg Room. --Marco Cavagna