Note that in the WebStorm version, instanceProperty was bubbled to the top of the list, whereas in IDEA the property remains in alphabetical order with all the other potential properties.
If I type a little more, you can see that IDEA does think instanceProperty is a better guess, as instanceProperty is bolded.
IDEA after typing ".instance"
I tried a couple different methods (adding the property in the constructor, prototypal extension, closure jsdocs) in the attached zip and got the same results in all instances. Is there a way to make IDEA perform like WebStorm in this regard, or should I submit a feature request?