This accident looks unusual. Certainly it doesn't look like a simple wire-strike to me and I'd be very surprised if the broken wires in the photo were anything other than collateral damage.
If the circumstances are as reported above by Gomer pylot, and it was an AP issue, on this type of aircraft (which is fully certificated for SPIFR btw), I can think of only two reasons why the autopilot would cause a rapid descent.
1. VS mode engaged with a large ROD set on the VSI.
2. An AP fault when the ALT mode was engaged.
I certainly wouldn't discount the second reason; I personally experienced this a number of times on an A109, albeit some years ago. Because it seemed to occur on a random basis it required in depth investigation, with the aircraft placed on ground power on jacks with the gear retracted for a prolonged period of time. Eventually the glitch was found and the AP computer was changed, which fixed it.