I got Chuckie Egg working!
There was still a problem in the interrupt handler. As I mentioned before the weekend, I had changed the behavour of IM 2 to make sure the program counter was pointing to (I * 256) + 0xFF. I discovered it should actually point to the contents of that location. Once that had changed it started working!
This has also given Chaos a new spurt of life. But it still seems to go a bit wrong when casting your first spell.
I also tracked down the bug that broke the teleports in Earth Shaker. The cause was a bug in the CPI, CPD, CPIR and CPDR instructions.
All in all, compatibility is getting better. I may move my focus to the two main items I want to complete before I release a beta… Snapshot loading and sound.