Maps are all organised on four giant 2D layouts. Rivertown, including the catacombs and sewers and all other basements is one map. Verdistis is another. The Council of Seven and the Wastelands are the other two. What you are seeing is monsters elsewhere on the map. The hearing skill doesn't check to see if the monster is in the same portion as you. So it's a negleted thing more than a bug.
Easter eggs are little hidden surprises the Easter Bunny plants in your garden each year. And the same has been translated into games. Easter eggs are any bonuses that you can find. Mostly they don't affect the game at all. They're usualy references to other stories, like the Romeo and Juliet thing mentioned above.
