Originally Posted by Pleiades

Whilst the dog bones (linkage plates) are under tension the vast majority of the time, if the suspension 'tops out' (hits the internal bump-stop in the shock) with any inertia, they will momentarily be under a significant compression force. I suspect that this is what has happened in Jon’s example? A combination of a high spring rate, low rebound damping and the action of a trailer’s weight pivoting and acting like a lever increases the chances of ‘topping out’. With a trailer, as the rear end of the bike rises, the trailer inclines backwards and all its weight will effectively shift rearwards, increasing upward leverage on the hitch, in turn further lifting the rear of the bike (extending the suspension) and with a greater magnitude of force/inertia. This is an exponentially increasing effect too; the more the rear suspension extends the greater the effect the trailer will have on extending it further.