It depends on the order of how BLOCK DEBUFF is placed on a champions Tool Tip.
For Example:
A hero can do BLOCK DEBUFF BUFF + NCREASE ATK BUFF
If the Increase Atk Buff is placed before the Block Debuff Buff on the hero, Your hero can be Frozen.
The game has a Tool Tip which puts the buffs on in a specific order.
Tormin can't freeze on or though BLOCK DEBUFF BUFF.
Tormin can freeze every other Buff.
And the Buff which your hero puts on first matters.
Here is a picture of Dark Elhain Skill.
I think your talking about the below skill:
---> Tormin Passive - Freezes Dark Elhain.
---> Dark Elhain Passive - Instantly removes the Freeze
---> Dark Elhain Passive - Puts up 3 New Buffs
---> The 3 New Buffs which get put on are Increase C.DMG - Increase C.RATE - Strengthen
---> Tormin Passive - Triggers Again - Freezes Dark Elhain due to 1 of the New 3 Buffs
---> Dark Elhain Passive - Is on 1 Turn Cool Down
---> Dark Elhain remains Frozen at this point.
And that is what your seeing.