I am using QCircularBuffer in my project and experienced a double free in certain circumstances.
The problem occurs on assignment copying the QCircularBuffer and append items afterwards to either one of the copies.

{
        Qt3DCore::QCircularBuffer<int> a(5);
        Qt3DCore::QCircularBuffer<int> b(5);
        b = a;
        b.append(3);
}

Here, buffer "a" hits a double free at the end of the scope in line 101, qcircularbuffer_p.h (development branch)

{ operator delete[](p); }