ui-router fires transition to root state as soon as controller loaded

Question

has anyone seen this sort of behaviour before ?

I have a button that is defined like this

<button ui-sref="designer({model: 'foobar' })">

I have a state defined as this

{
  name: 'designer',
  state: {
    url: 'designer/:model/:form',
    templateUrl: '/partials/designer.html',
    controller: 'DesignerController',
    controllerAs: 'designer'
  }
}

and a controller like this

(function() {
    angular.module('myApp')
        .controller('DesignerController', DesignerController)

    function DesignerController() {
        console.log("-->loaded designer");
    }
})();

when I click on the button, I get this in the console (I've added some debugging)

$stateChangeSuccess to designer- fired once the state transition is complete.

-->loaded designer

$viewContentLoaded - fired after dom rendered Object {name: "$viewContentLoaded", targetScope: ChildScope, defaultPrevented: false, currentScope: Object}

$stateChangeStart to undefined- fired when the transition begins. toState,toParams : 
 Object {url: "/", templateUrl: "/partials/main.html", name: "root", status: "exited", onExit: undefined} Object {}

$stateChangeSuccess to root- fired once the state transition is complete.

as you can see - as soon as the designer controller is loaded, a transition to the root state is fired - what can cause that ?