stat.timeSinceDeath goes twice as fast in adventure mode

When you create an objective with target criteria type "stat.timeSinceDeath":
scoreboard objectives add testObjective stat.timeSinceDeath

Then setup a 20hz clock, with one command block saying:
scoreboard players add test testObjective 1

You will see the numbers go up equally fast when in creative or survival, BUT when you switch to adventure gamemode, the players score will go up twice as fast.