Setting Window-Specific behaviour

[Alvin]

I want to set the following:

Every Konsole windows should have an opacity of 90%.

I suppose this is done in System Settings > Window Behavior > Window-Specific. 
Only problem is that I've never got it to actually set the opacity to 90%, so 
I must be using the wrong configuration.

This is what I've tried:

Window:
	Description:	Set Konsole Opacity to 90%
	Window class:	Konsole
	Exact Match
Preferences
	Active opacity in % - Force Temporarily - 90

What did I miss?

-- 
Kind regards,
Alvin