Issue with switching from one demo to another

[limonte]

flush.html:35 Uncaught TypeError: Cannot redefine property: _element
    at Function.defineProperty (<anonymous>)
    at HTMLElement._mappedObjectChanged (px-data-grid-column.html:153)
    at Object.runObserverEffect [as fn] (property-effects.html:214)
    at runEffectsForProperty (property-effects.html:159)
    at runEffects (property-effects.html:125)
    at HTMLElement._propertiesChanged (property-effects.html:1703)
    at HTMLElement._flushProperties (properties-changed.html:338)
    at HTMLElement._flushProperties (property-effects.html:1551)
    at HTMLElement.ready (property-effects.html:1656)
    at HTMLElement.ready (element-mixin.html:546)