Heap corruption happens due to double memory release when QDomAttr::setNodeValue is called.

HEAP[QDomAttr_DoubleRelease.exe]: HEAP: Free Heap block 0000023C5B729CE0 modified at 0000023C5B729D28 after it was freed

void QDomAttrPrivate::setNodeValue(const QString& v)
{
    value = v;
    QDomTextPrivate *t = new QDomTextPrivate(nullptr, this, v);
    // keep the refcount balanced: appendChild() does a ref anyway.
    t->ref.deref();
    if (first) {
        delete removeChild(first);  // <--- This deletes without checking the reference count of the return value of removeChild
    }
    appendChild(t);
}