From my H16 sailing days: I remember, if I raked the mast aft too much it would cause the mainsheet to be angled aft (slightly), when I sheeted in, it would cause the boom to push foward causing the mast to over rotate. It happens in my F16 now as well. Good thing the F16 has mast rotation control.
But check on the H16 that the mast is NOT rake aft too much, if not move the mainsheet a few inches foward on the boom.
What happens is the mainsheet can PUSH the boom foward, cause the mast to over rotate.
Hope that helps