Activator rails' hardness seems to be slightly lower than other rail types. This causes them to be broken slightly too quickly (~16 game ticks instead of 20-21). According to the wiki an activator rail is supposed to have a hardness of 0.7 (same as other rails). I haven't been able to determine the hardness used in MCPE but it is certainly lower than it should be.

This bug was discovered due to it tripping anti-cheat on a custom server, but it is also reproducible in a vanilla game by placing an activator vs any other type of rail, then breaking them in survival. If you watch carefully you'll notice that the activator rail breaks slightly faster than the other rail.

Other rail types are not affected by this bug.