When you select a-scene and copy entity to clipboard, this is exported

    <div class="a-loader-title" style="display: none;">Example Scene</div></a-scene>

It shouldn't be exported.
That's probably a fix to do in aframe actually to add the aframe-injected attribute, see
https://github.com/search?q=repo%3Aaframevr%2Faframe%20AFRAME_INJECTED&type=code