QToolTip QSS style rule doesn't clip background color as per border-radius property setting

Is it by design that a QToolTip widget can only be rendered with a background color as a rectangular box with pointy edges, even if one sets the border-radius property for the widget to, say, 4px?

I have this QSS style rule, which renders the border with a 4px radius just fine, but the background color (which is inherited from its parent QLineEdit widget) does not clip to the border radius, so there appear triangle-like artifacts at the 4 edges of the tooltip widget, which as a whole looks really ugly.

QToolTip {
  border: 1px solid #386b6b;
  border-radius: 4px;
  font-size: 15px;
  font-weight: bold;
}

However, the QLineEdit widget looks sleek with its rounded corners, and its QSS style rule is defined like this:

QLineEdit {
  background-color: #223a3a;
  border: 1px solid #386b6b;
  border-radius: 4px;
  color: #c5e0e0;
  font-size: 15px;
  font-weight: bold;
  max-width: 600px;
  min-width: 600px;
  qproperty-alignment: AlignCenter;
}

I tried many things, like adding background-clip and many other possible solutions. I've asked ChatGPT and also Claude AI to help me, but no solution worked. It is strange that setting the border-radius property for the QToolTip QSS style rule is not respected at all.

So, I gather, this must be a bug (or a deliberate design?) of Qt. I am using PySide6, but this stems from Qt itself, so I am writing a bug report for Qt.