Radio interface gets stuck

[BrechtDeMan]

Try here (master branch)

In the radio interface example, complete the first page, then click Next: nothing happens (still Page 1 of 5, radio buttons still selected).
Console error:

NotFoundError: Node was not found (core.js:2655)
    Interface/this.commentBoxes</commentBoxes.deleteCommentBoxes/< (http://localhost:8000/js/core.js:2655:21)
    forEach self-hosted:271:13 Interface/this.commentBoxes</commentBoxes.deleteCommentBoxes (http://localhost:8000/js/core.js:2654:17)
    Interface/this.newPage (http://localhost:8000/js/core.js:2372:9)
    stateMachine/this.advanceState (http://localhost:8000/js/core.js:1398:17)
    stateMachine/this.advanceState (http://localhost:8000/js/core.js:1419:21)
    advanceState (http://localhost:8000/js/core.js:1229:5)
    interfacePopup/this.initState (http://localhost:8000/js/core.js:1142:13)
    stateMachine/this.advanceState (http://localhost:8000/js/core.js:1413:25)
    buttonSubmitClick (http://localhost:8000/interfaces/discrete.js:538:9)

Then, when clicking any of the 'Play' buttons, no sound and the following error:

TypeError: this.audioObjects[id] is undefined [Learn More] (core.js:1769:13)
    AudioEngine/this.play (http://localhost:8000/js/core.js:1769:13)
    discreteObject/this.play.onclick (http://localhost:8000/interfaces/discrete.js:297:13)

Browsers tested:

• Firefox 58.0.2
• Chrome 65.0.3325.181
• Safari 10.1.2

Branches tested:

• master (last commit)
• dev_main (last commit)