You Left Us Behind
To say that Morgana and the others were unhappy with Karl taking off without half his team was an understatement.
It didn't quite violate the terms of their agreement, as the rest of the team was technically on their way to the battle and might have made it if the battle lasted longer, but he was pushing his luck, and he had left without his healers and support.
The fact that Karl came back into camp covered in ash and reeking of burnt Giants, while his companions were soaked with blood, was not lost on anyone, students or otherwise. The team had gathered at the back near the bus, and the looks that they were giving the trio said more than any words they could come up with.