There's also an occasional issue with some of the melee husk things (name escapes me, but the deformed humans) that if they are in certain areas of a map, most notably the large gray walls common on Farm maps, that it hard locks the game when you do lethal damage. Not sure if there's anything you can do about that but figured I'd mention it.
Edit: Also, yeah .26CE save games aren't backwards compatible with any other CE version.