Getting different url requests to API depending on how I've gotten to the page

I'm getting some curious behaviour that I can't figure out the reason for.

This is my router:

App.Router.map(function() {
    this.resource('mapPieceSets', { path: '/map-pieces' }, function () {
        this.resource('mapPieceSet', { path: '/:mapPieceSet_id' }, function () {
            this.resource('mapPiece', { path: '/:mapPiece_id' });
        });
    });
});

I reload the app from the home page #/ then navigate down to the mapPiece route, I get these URLs requested:

• [Domain]/api/mapPieceSets/


• [Domain]/api/mapPieces/1/


• [Domain]/api/mapPieces/2/

And it all works fine (mapPieceSets returns a list of mapPieceSet which have a list of mapPiece against them)

However, if I reload the whilst on a mapPiece routed page, then I get this URL:

• [Domain]/api/mapPieceSets/


• [Domain]/api/mapPieceSets/?mapPieceSet_id=1


• [Domain]/api/mapPieces/?mapPiece_id=1

So switching from /:id= to ?id=, which isn't working on my end points (that's a side issue which I need to resolve), but just wondering why the URLs changed what they're requesting, and why we get a request to mapPieceSets/?mapPieceSet_id=1 when the whole of that object is returned within the response from mapPieceSets/

(If you need any other snippets of code from my app, let me know and I can put them in)