[davidmanze]

I don't think anything could have fried on the sensor, as you can't actually reach the sensor from the front without passing through more optical filters.

 

I have to wonder if the sun could still be the culprit. The mirror will reduce the intensity, but as it isn't focused on the mirror itself that wont take the worst of the heat. If anything, perhaps a slight misfocus at the time would make the shutter a more likely target? If the sun were in perfect focus on the sensor, even the small distance to the shutter would give a defocus effect and may reduce the chances of it burning.

 

Given all this, I have to say I've shot directly at the sun with various lenses before without ill effect. I did try to keep the duration the sun was in view to a minimum though. Maybe a longer period is required.

  As have I, a strange one, even the shutter would be in front of the focal plane reducing the heat concentration and the hole was quite a decent size and  it is at the upper part of the shutter, with the image inversion the hole would be in the lower half (from the sun) and as you say behind the mirror..........  hmmm...  in live view the shutters open, even with a long exposure the shutters open and leaves only the short time between the mirror rising and the shutter opening......with the  mirror in lock up  the camera would be on a tripod, a long wait before the exposure maybe with the sun in the lower frame or in portrait?  that's really the only way!   would you forget to mention mirror up on a tripod?

 

 seriously weird, maybe I'm back to my electrical theory, or not!