climbed stairs twice and got index out of bounds

[kagan019]

java.lang.ArrayIndexOutOfBoundsException: Index -257 out of bounds for length 65536
at com.jdh.microcraft.level.Level.tick(Level.java:492)
at com.jdh.microcraft.GameState.tick(GameState.java:128)
at com.jdh.microcraft.Main.tick(Main.java:79)
at com.jdh.microcraft.util.Window.loop(Window.java:177)
at com.jdh.microcraft.Main.run(Main.java:54)
at java.base/java.lang.Thread.run(Thread.java:832)

immediately upon returning to the surface. I was carrying a lantern. sometimes a damage number appears when I climb stairs...

I also have trouble de-equipping iron armor to equip gold.