List view repeated with restapi sync adapter

I am making use of restapi sync adapter

exports.definition = {
    config: {
 
      //  "debug": 1, 
        adapter: {
            type: "restapi",
            collection_name: "job"
        }
    },
    extendModel: function(Model) {
        _.extend(Model.prototype, {
 
        });
 
        return Model;
    },
    extendCollection: function(Collection) {
        _.extend(Collection.prototype, {
            // extended functions and properties go here
            url:function(){
                var Offset=this.length;
                console.log('The length::',this.length);
                return 'http://www.xxxxxxxxx/job.php/fetchjobs?offset='+Offset;
            }
        });
 
        return Collection;
    }
};

alloy.js

var jobCollection = Alloy.Collections.instance('job');

~~~ xml file:

<ListSection id="section" dataCollection="job" >
<ListItem  jobDescription:text="{post_name}" startDay:text="{job_start_day}"  startMonth:text="{job_start_month}" wages:text="{job_wages}"></ListItem>
</ListSection>

controller:

jobCollection.fetch({
        reset:false,
    success: function(collection, response, options){
        Alloy.Globals.hideIndicator();
 
 
       console.log('print first');
       console.log(collection.length);
       console.log(JSON.stringify(collection));
       collection.each (function (oneModel){
        console.log(oneModel.get('post_name'));
       });
       // Set the initial item threshold    
$.listView.setMarker({sectionIndex:0, itemIndex: (jobCollection.length-1) });
    },
    error: function(){
        console.log('wrong print');
    }
});
 
 
 
$.listView.addEventListener('marker', function(e){ 
 
    jobCollection.fetch({
        remove : false,
        add : true,
        reset : false,
    success: function(collection, response, options){
 
   //   Alloy.Globals.hideIndicator();
        console.log('print second');
       console.log(jobCollection.length);
       console.log(JSON.stringify(collection));
       collection.each (function (oneModel){
        console.log(oneModel.get('post_name'));
       });
       $.listView.setMarker({sectionIndex:0, itemIndex: (jobCollection.length-1) });
    },
    error: function(){
        // something is wrong.. 
    }
 
});
 
});

The collection url fetches 5 new jobs at a time,for values of offset 0,5,10 and so on. Hence here it is taking the offset as zero then five and then ten. But the offset value of 10 gets repeated after i drag to tenth record and this goes on infinitely. At the same time the length of the collection remains at 10 when actually it should have been 15 and then no more records would be fetched. Doubt my setMarker is causing an issue here Let me know if you need anything else on this.