Ah, random physics. Nothing like spending several minutes restarting a stage and shooting the same spot over and over again until the chunks decide to fly/fall *just* right.
I like how I'll have four Level 2-3 soldier towers built around a choke point and two monsters will just dance past merrily as every single other soldier attacks the third monster.
"Change" should change occupations in the same career tree at the current tier. If it is just going to start the character over, then it may as well be "Delete"