Ha ha... zebras shown on sky and roof.. I wll try again! 
I guess these were YUV-based zebras, not RAW.
The YUV (JPEG) overlays are known for
false positives when checking for overexposure.
Also RAW graph on bottom showed over!
This one might be a bug in the raw histogram; can you expose in the same way and then select Debug -> Dump image buffers?
The 99.99 percentile in your second 7D example is at 13281; to display "OVER", this value should be above 15000 on 7D. Maybe the weather just got darker when you captured the snapshot?