TrinityCore/TrinityCore — pull request #7210 by Chipsi (2012-07-28 13:57:47+00:00)
Title: Core/Spells: Spells with SPELL_EFFECT_KNOCK_BACK(like Thunderstorm)

Proof:
http://www.mmo-champion.com/threads/611960-Resisting-Thunderstorm/page2

Ok, just did some basic testing and this is what i can tell you so far

Stunned Targets (tested with warstomp and stoneclaw proc): Take damage, no knockback effect
Rooted Targets (tested with frost nova): Take damage, no knockback effect
Snared Targets (tested with earthbind totem): Take damage, take full distance knockback (not a decreased effect to do snare slowing)
Iceblocked Mage: Immune to both damage and knockback effect.
Feigned Death: Deals full damage and knockback effect
Polymorphed Target: Deals full damage and knockback effect, breaks the CC.
Freezing Trapped Target: Deals full damage and knockback effect, breaks the CC.
Feared Target (tested with Hunter's Fear Beast): Deals full damage and knockback effect, Has a chance to break the Fear just like any other direct damage spell.
Slept Target (tested with Hunter's Wyvern Sting): Deals full damage and knockback effect, breaks the CC.