Quicksand:
I have to desagree with your comments about retrimming. There are a lot of examples of why you may need to make trim corrections, but I'll sight the easiest and best example:
FUEL
The fuel tank on most models is ahead of the CG. With a full tank you need a little more up trim than with an empty tank. With my GP Ultimate for example my elevator trim at the start of the flight is 2 clicks up. At the end it is neutral. I'm picky and could live without making the adjustment, but it's there.
As I said previously, though, if you need to make big trim changes between or during a flight then something's wrong, and you're right there may be some linkage issues.