Since at least 1.9, there has been a bug with the animations, mostly the sort that you end up stuck in an animation when you teleport from one place where you initiate the animation, to a destination. It doesn't automatically flush your animations.
This also has another side effect: When sitting on objects that are rezzed in and moved, and then de-rezzed, the sim has a habit of crashing.
I have a sort of 'elevator' that takes an avatar from the ground up to a point in the air, and another that brings them back down. This platform rezzes a temporary object, which the avatar can sit on. Upon sitting, it initiates the sit animation and the prim begins moving to its destinaton. Upon reaching the destination, it is supposed to boot the avatar off and de-rez. This works SOMETIMES, othertimes, it crashes the sim! I've crashed the Moore sim at LEAST three times today, and a few random times over the last few weeks. This might merit looking into.