Tree man has all four squares in Acid (Stop terrain). At his first square he should be half in and therefore stop, but he just keeps going like he's not in it at all.
I was going to but how do you take a screenshot of something that didn't happen? You use ASCII art! X = Acid terrain t = Tree Man on Acid Terrain T = Tree Man not on Acid Terrain . = empty square tt.... tt.... then XX..TT XX..TT Like either a) He jumped to target. or b) After the first square his center point wasn't in acid so he ignored it or c) He only checked the square he was moving in to for acid and didn't check his trailing two butt squares. How dat?