Applied Color Science compares "black sun" effect between Omnivision OV5610 and Micron MT9P401, both 5MP. It occurs when a camera is pointed at a scene with a very bright, very concentrated source of light like the disk of the sun. Some CMOS sensors show these super-bright areas as dark, rather than saturated bright.
The result of the comparison is that MT9P401 sensor is free from bright image inversion, while OV5610 suffers from it. One needs to note that Omnivision's sensor belongs to 2.8um pixel generation while Micron's is 2.2um. The newer Omnivision sensors might behave differently. The site also has a simplistic explanation of why "black sun" happens.