QQuickPaintedItem with FramebufferObject and HighDpiScaling does not scale properly

Having set setRenderTarget(Image) onto a QQuickPaintedItem results in having painter's viewport in the QQuickPaintedItem::paint() pure virtual method as large as the content size, in pixels. It seems fine, as painter->device()>devicePixelRatio() returns 1. When I set render target to FramebufferObject, my item is painted in user-space pixels, meaning that my rendered image is scaled by the devicePixelRatio. As painter>device()->devicePixelRatio() still returns 1, I'd expect it to behave exactly the same as is does when rendering to image.
QQuickPaintedItem::setTextureSize() does not help, as it always raises QOpenGLFramebufferObject: Framebuffer incomplete attachment. error.