let go of tiller, cookies ensue

Again from our Fabulous Forums…
I’ve read hundreds of times over the years “if your boat is properly trimmed, you’ll have a little bit of weather helm. If you let go of the tiller, it will turn into the wind on it’s own and stop”
So today I was out playing around on my Merit 22. Probably 8 knot winds, nothing too exciting. Headed up close hauled, I let go of the tiller. Soon the tiller was all the way over, and the boat spins through the wind, the genoa backs, the boat turns downwind, jibes, spins upwind again, and repeats. Just endless cookies.
This was under the main and a Genoa, probably 140%.
Have I been lied to, or is my boat/sail balance just really out of whack?
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