[SalesForce] Returning an object from an AuraEnabled method with properties named r or s

When you run the code below, everything works as expected. The console logs an object with all of the a-z properties minus r and s of course since they are commented out.

If you uncomment s, the console logs 118 – just the number, not in an object. When you uncomment r, the console logs undefined. There is no issue with using any of the upper-case letters.

Does anyone have any theories on why lower-case r and s would be causing this issue?

// Client-side controller

({
    handlePress : function(component, event, helper) {
        var action = component.get("c.returnClassic");
        action.setCallback(this,function(response){
                if (response.getState() === "SUCCESS"){
                    console.log(response.getReturnValue());
                }
            });
        $A.enqueueAction(action);
    }
})

// Server-side controller

public class LightningController {

    public class Classic{

        @AuraEnabled public Integer a {get; set;}
        @AuraEnabled public Integer b {get; set;}
        @AuraEnabled public Integer c {get; set;}
        @AuraEnabled public Integer d {get; set;}
        @AuraEnabled public Integer e {get; set;}
        @AuraEnabled public Integer f {get; set;}
        @AuraEnabled public Integer g {get; set;}
        @AuraEnabled public Integer h {get; set;}
        @AuraEnabled public Integer i {get; set;}
        @AuraEnabled public Integer j {get; set;}
        @AuraEnabled public Integer k {get; set;}
        @AuraEnabled public Integer l {get; set;}
        @AuraEnabled public Integer m {get; set;}
        @AuraEnabled public Integer n {get; set;}
        @AuraEnabled public Integer o {get; set;}
        @AuraEnabled public Integer p {get; set;}
        @AuraEnabled public Integer q {get; set;}
//        @AuraEnabled public Integer r {get; set;}
//        @AuraEnabled public Integer s {get; set;}
        @AuraEnabled public Integer t {get; set;}
        @AuraEnabled public Integer u {get; set;}
        @AuraEnabled public Integer v {get; set;}
        @AuraEnabled public Integer w {get; set;}
        @AuraEnabled public Integer x {get; set;}
        @AuraEnabled public Integer y {get; set;}
        @AuraEnabled public Integer z {get; set;}

        public Classic(){
            a = 97;
            b = 98;
            c = 99;
            d = 100;
            e = 101;
            f = 102;
            g = 103;
            h = 104;
            i = 105;
            j = 106;
            k = 107;
            l = 108;
            m = 109;
            n = 110;
            o = 111;
            p = 112;
            q = 113;
//            r = 114;
//            s = 115;
            t = 116;
            u = 117;
            v = 118;
            w = 119;
            x = 120;
            y = 121;
            z = 122;
        }

    }

    @AuraEnabled
    public static Classic returnClassic(){
        return new Classic();
    }

}