I was curious as to why Burnside only crossed with a couple of units which exposed them to being surrounded. That seemed like a really bad scripting. Taking a peek at the actual scenario answered the question. Burnside's Corps isn't released until 8 AM. What crossed was a couple of units that the Rebel units triggered the release of because they got to close to them. Script kicked in and they made a suicide charge. Scripts will force units to move but won't make them any smarter once they get in contact.
