Hi Chris,
I was thinking about what you said on Friday about this. I don't remember seeing a capacitor on Neil Craggs B4 attached to his receiver, but I am sure he had one attached to the power wires on his Speedo. This maybe what is causing your problems, but it might be worth checking the manual. I know my novak said that you MUST always use one, and when I didn't on my old Novak Cyclone, I had terrible dumping problems for some reason (this was with 2000 cells mind), but once fitted the problems went away.
http://www.oople.com/rc/photos/works.../OOP_7789.html
It is jus to the right of the speedo in the above pic.
HTH
Mark