QGraphicsSvgItem appears two times after adding to scene and moving it

[fer-rum]

Hello everyone,
It seems like a simple thing, but I could not find a solution to the following problem. Maybe I am missing somthing obvious, but it would be great, if you could point out what else I can check to solve this.

Problem description:
I do have a scene, which contains a QGraphicsSvgItem as a child of a custom made QGraphicsObject.
After adding, the position of the new child is off, so I use moveBy(…) to correct that and recalculate the parents boundingRect to include the child as well.

But after doing so, I do have the child drawn twofold in the scene: Once at the position it was initially added and once in the position it was moved to. I tried updating and redrawing the whole scene, but nothing seems to change.

Code:
The function that seems responsible for the issue. I abbreviated some irrelevant things, to focus on the main problem. You can however find the full code at github.

 ModulePortGI::ModulePortGI(…) : PortGraphicsItem(…) {
 int moveX;
 int moveY;
 QGraphicsSvgItem* decal;
 switch(direction) {
case model::enums::PortDirection::OUT :
    decal = new QGraphicsSvgItem(":/…/outside_port_out.svg", this);
    moveX = 0;
    moveY = -decal->boundingRect().height()/2;
    break;
case model::enums::PortDirection::IN :
    decal = new QGraphicsSvgItem(":/…/outside_port_in.svg", this);
    moveX = -decal->boundingRect().width();
    moveY = -decal->boundingRect().height()/2;
    break;
default : // should not happen
    Q_ASSERT(false);
}
this->addActual(decal);
Q_ASSERT(decal->parentItem() == this);
decal->moveBy(moveX, moveY);
this->recalculateBoundingRect();
}

The function addActual(…) is defined in a base class SchematicElement as

void
SchematicElement::addActual(QGraphicsItem* actual) {
    m_actuals.append(actual);
    actual->setParentItem(this);
    this->recalculateBoundingRect();
}

This also is the case for recalculateBoundingRect(). (Which I found to be working as expected, so I leave that out.)

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So, what else could I check to get this sorted out?
Thanks in advance.