Yeah, that will always get called b/c it's just another listener in the chain. In your button config, add a 'click' property which is the handler.
Look at the feedviewer example to see more of this. Note also, that in 1.0 'click' changes to 'handler' and you don't have to do the createDelegate - it's done for you.
, className: 'mx-toolbar-button'
, id: view.getId() + '-wdr-compose-attach-button'
, disabled: false
, click: this.handleAttach.createDelegate(this)