Preserving border / antialiasing QWidget on a QGraphicsProxyWidget

[sedi]

Hi,
I have a QWidget, filled with some QPushButtons and QComboBoxes, which lives in a QGraphicScene, as courtesy of a QGraphicsProxyWidget.
When i scale the QGraphicsView to a smaller size there are a few ugly things.

I expected these (good old Nyquist), but I also expected to get rid of them (more or less) with a good antialiasing:

view = new QGraphicsView(scene);
view->setRenderHints(QPainter::HighQualityAntialiasing|QPainter::TextAntialiasing);
view->scale(0.9,0.9);

view = new QGraphicsView(scene);
view->setRenderHints(QPainter::HighQualityAntialiasing|QPainter::TextAntialiasing);
view->scale(0.9,0.9);

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Additionally I could improve my PixmapItems this way:

this->fotoPixmapItem->setTransformationMode(Qt::SmoothTransformation);

this->fotoPixmapItem->setTransformationMode(Qt::SmoothTransformation);

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Now the Pictures look ok, I can live with some rather ugly text antialiasing, but...

...I still have a problem with my widgets:
Here you see a screenshot snippet of a QCombobox which lost its left black border line:
Qcombobox.jpg
FYC I have attached an enlarged (4 times, Photoshop) version of the same screenshot in the attachments.

Is there any way to ensure that the border line is at least one pixel wide? Or to set up a better antialiasing for the widgets? I want the view to be user scaleable to better fit onto various screen sizes. Is scaling perhaps a stupid Idea in the first place?