If set to false then automatic disable processing of the Icon will not be done.
In the PreProcessStyle event then this will always come as true, but you can set it to false if you want to for example have different Icon for disabled or if you want to process the Icon shading your self.
If wanting to process disabled icon your self then in the PreProcessStyle event detect Disabled, then set this property, and set the Icon property as well.
This property currently applies when used with:
CustomButton