This is related to the Max sample intensity (MSI) parameter. 

The Max sample intensity parameter is relative to the current color mapping, so starting rendering with different exposures will result in different max sample intensity value, and in turn, different amount of bias in the picture. For example, Max sample intensity value 10 should result in the same amount of bias in both dim and bright interior shots. But once you change exposure after the rendering has started, you cannot change the already rendered bias.

Examples

MSI is set to 1 to enhance the effect. Using default value or higher should not produce such dramatic differences. 

Image A

MSI = 1
Exposure = 1
Image rendered with exposure = 1
Note: image looks different than image B although technically their exposure and intensity values are the same

Image B

MSI = 1
Image rendered with exposure = 5, then exposure changed to 1 in VFB
Note: image looks different than in example A although technically their exposure and intensity values are the same

Image C

MSI = 1
Image rendered with exposure = 1, then exposure changed to 5 in VFB
Note: image looks different than in example D although technically their exposure and intensity values are the same

Image D

MSI = 1
Image rendered with exposure = 5
Note: image looks different than in example C although technically their exposure and intensity values are the same

See also: MSI