I'm not a Canon shooter but your image defect is almost identical to the visual symptoms experienced by a900/a850 shutter failures.
Just asking, since I'm not familiar with the A900/a850, are those symptoms vertical streaks like in the OPs images? One would expect horizontal artifacts with horizontal shutter related issues. Also, brighter areas would require the shutter to slow down in mid travel, which seems unlikely. Shutter bounce defects are usually visible at the end of the curtain path, at the edge of the image, over the full length.
What the OP is showing looks like an internal specular reflection, maybe something in the mirror chamber that gets hit when facing a bright point lightsource (from the backlit subject). The location within the frame should give a clue (just remember the image projection is upside down).