On 26 December 2012, a Norwegian Air Shuttle Boeing 737-800 intercepting the ILS GS at Kittila with the AP engaged experienced an uncommanded pitch up in IMC. Crew response did not prevent rapid development of a very high nose up attitude and, as airspeed dropped rapidly whilst climbing, stick shaker activation occurred. Recovery from the upset was eventually achieved and there was no recurrence. The Investigation is continuing but initial findings are that the normal operation of one of the elevator PCUs had been compromised by ground de-ice fluid residue and that all Boeing 737 variants may be vulnerable.