QJsonObject memory corruption

Creating an empty object in an object, retrieving it for modification creates a memory corruption.

The following code reproduces will randomly segfault (or display a corrupted item):

#include <QJsonObject>
#include <QDebug>

int main() {
  QJsonObject parent;
  QJsonObject child;

  parent["child"] = child;
  child = parent["child"].toObject();
  // here we should have { "child": { } }

  child["test"] = "test";
  parent.insert("child", child);
  // here we should have { "child": { "test" : "test" } }

  qDebug() << parent;
}

Note: test fails only if child is an empty object when inserted
Note: test fails only if child is retrieved from parent before being modified
Note: commenting-out Data::compact code in qjson.cpp removes the issue (seems to be related to is_object flag)

Is there any incorrect use of QJsonObject in the above code ?