Fuji - I think that either somebody (not you) is taking the p*ss out of me as usual, or we are talking with wires crossed.
Nope, you have just become paranoid.
I still maintain and so does my engineer that any aircraft that descends into th spiral of death that you are indicating is probably down to being miss-rigged or miss-loaded.
I have just done a flight test in a Chipmunk and lo and behold, trimmed it out straight and level and flew along for several minutes in a straight line with out any inclination to start a turn or head for a dive.