Stun duration: *some player-cast stuns are capped at 4 seconds

[Skru]

As a cleric I see I have some stuns that lasts longer than 4 seconds. However in the wiki it says the following for example for the spell Enforced Reverence:
Stun for 8.0* seconds up to level 55 (*some player-cast stuns are capped at 4 seconds)

I tried to look around but I couldn't find out where the (*some player-cast stuns are capped at 4 seconds) might apply.

Do anyone of you guys know what type of mobs would cap it to only 4 seconds?