Bit of bad news. I'm generally very careful with my equipment so I'm absolutely flabbergasted as to how this happened. We were away for a few days which involved both train and airplane travel.
The camera when not in my hands travel inside a very well padded large camera bag with the camera in it's own compartment separated from any lenses. I did not have a flash with me for the trip and noticed the damage yesterday when changing lenses. It must have received a knock somewhere along the way but as to how this could happen through a well padded camera bag I'm not sure. I've not knocked the camera against anything.
I have contacted the New Zealand Pentax service agent this morning and am waiting to hear from him with regards to costs to get this sorted. The camera will likely need to go to Japan to have this fixed.
From an online search it seems the top plastic is very thin. If you have a K-1 I'd advise taking extreme care with the top of the camera! I'll post more when I know more.