At this point I think you should do a camera reset again.
After the reset you should turn the camera off.
Then turn the camera back on again.
This is necessary to complete the reset.
There is EXIF information included in every picture.
This information includes details about the picture.
Find one of the dark pictures where the flash did fire.
With the computer, Right click on the file name.
Then click on Properties.
Click on the Detail tab.
There will be data about shutter speed, aperture, ISO, etc.
I would like to know all of that information.
Take a few pictures outdoors (without flash) and let me know how they came out.
Auto flash with/without red-eye enabled will likely react the same. With red-eye, it will flash twice.
So far I have not found anything about a person surrounded by a frame.