Hmmm.... Well I have hacked the kernel so that when I set a rate of 2400 in my application it actually sets it to 1500 in serial_sa1100.c. i.e. I'm not relying on config.ini at all anymore.

It seems to work in the sense that my PC at 1500 baud gets the data correctly, but the changer doesn't understand it whereas the changer understands the PC fine. I need to put it on a DSO and see if there's something obvious. I'm pretty sure I have it at 8N1 correctly etc.