System Information
win 7 / gtx 1070

Blender Version
2.79 official and 65d40b3 or lastest build as of toaday

Short description of error
When save buffers is checked in performance tab it looks like the exposure form color management is applied twice while rendering but only once when rendering is finished

To reproduce :
With cycles render and just a background , set exposure above 0 (ex:2) and 512 samples (to be sure to have time to see the difference, check save buffers, hit F12.
Rendering is much brighter while rendering than finished picture.