The following sequence will trigger an assert during the second QPainterPath::moveTo() call:

QPainterPath p;
p.moveTo(0., 0.);
p.clear();
p.moveTo(0., 0.);

The second moveTo() triggers this assert:

QPainterPath::moveTo()
{
    ...

    ensureData();
    detach();

    QPainterPathData *d = d_func();
    Q_ASSERT(!d->elements.isEmpty());

    ...
}

This is because the call to clear() has cleared all the path elements, including the initial MoveTo, but data still exists so it's not re-initialized by the previous ensureData() call.

Maybe QPainterPath::ensureData() shall insert a first null MoveTo element when the d-pointer exists but has empty data (which is the state it's in after a clear).

Or QPainterPath::clear() shall ensure that the path data contains at least a null MoveTo if it's not null.