vsync caused Time stuttering

Hello, I have got problem with vsync. When I set "Every V Blank" option in QualitySettings i get seemingly random stutter(everything directly dependendent on Time.* functions slows down severely in selected frames(viz image from profiler-sharp peaks after selection)). Profiler shows, that most of the time(yellow wall) is vsync's WaitForTargetFPS, but for some frames there is litteraly no wait at all for couple of frames. this happens in all builds i tryied: Android build on samsung galaxy I3, WebGL build and in unity editor. when vsync is turned off then profiler shows aprox. 1000FPS, so this should not be problem with rendering, caching or buffering. I dont get it. It even happens for Time.time and Time.realTimeSinceStartup which i would expect to be completely independent of vertical sync.

Any help is appreciated. thanks