This is related to IDEA-8325 as it referrs to the same pattern of usage.
Take:
function Class1(){
this.variable = 3;
}
Class1.prototype.method1 = function() {
this.variable; // autocomplete works here
}
Class1.prototype.method2 = Class1_method2;
function Class1_method2() {
this.variable; // autocomplete does not work here
}
Variable autocomplete only works when you define a function anonymously as for method1, not by assignment as per method2.