Your target is immune to the stun portion of this effect.
 

I remember back on live that weapons like Sceptre of Destruction, Veldrak's Shortblade or any other weapon that had a stun + DD gave the message "Your target is immune to the stun portion of this effect."

Example:

Wielding Veldrak's Shortblade. Effect: Static Strike

King Tormax was hit by non-melee for 179 points of damage.
Your target is immune to the stun portion of this effect.

Is this not in Project 1999? I have yet to notice this. Pretty sure this was within Velious era.

It is... source used a T-staff:

[Mon Aug 10 20:25:52 2015] Your target is immune to the stun portion of this effect.
[Mon Aug 10 20:25:52 2015] Gkrean Prophet of Tallon was hit by non-melee for 120 points of damage.
[Mon Aug 10 20:25:52 2015] Gkrean Prophet of Tallon begins to spin from one hundred blows.