You see this in your inspector because you have the option activated to "Show Shadow DOM". You find this setting in the general settings tab under the "Elements"
If you deactivate it. These fragments will disappear from your inspector
Shadow DOM is internal to the element and hidden from the end-user. Its nodes are not children of <my-custom-element>
or <input>
or ... (http://www.polymer-project.org/platform/shadow-dom.html#shadow-dom-subtrees)
You will find more information here: