I've been having problems with the MESS emulator, so I decided to go back to the known-good cartridge images. The plan was to decompile the image, then compile the assembly output and compare the two images. I'm glad I did that since I found a problem with class VII instructions. I was adding extra arguments in some cases and not using trailing immediate 16-bit words on others. So now there are three variant of class VII instructions, and everyone's happy.