QPrinter pageLayout().paintRect not working correctly

1) Start in portrait mode and set page margins:

qDebug() << printer.pageLayout().pageSize().rect(QPageSize::Millimeter);

OUTPUT: QRectF(0,0 210x297)

bool b=printer.setPageMargins(QMarginsF(20,30,40,50), QPageLayout::Millimeter);
Q_ASSERT(b);
QRectF r_portrait=printer.pageLayout().paintRect(QPageLayout::Millimeter);
qDebug() << printer.pageLayout().paintRect(QPageLayout::Millimeter) << printer.pageLayout().margins(QPageLayout::Millimeter);

OUTPUT: QRectF(20,30 150x217) QMarginsF(20, 30, 40, 50)

2) Set orientation to landscape mode:

auto pageLayout=printer.pageLayout();
pageLayout.setOrientation(QPageLayout::Landscape);
b=printer.setPageLayout(pageLayout);
Q_ASSERT(b);
qDebug() << printer.pageLayout().paintRect(QPageLayout::Millimeter) << printer.pageLayout().margins(QPageLayout::Millimeter);

OUTPUT: QRectF(20,30 237x130) QMarginsF(20, 30, 40, 50)

I would assume:

QRectF(30,20, 217x150)

One practical example: I used the "Canon E410 series" dot-printer as test printer. The physical margins are: (3.39, 2.96, 3.39, 16.72).

I want to stretch a picture on the whole paint area in landscape mode, but with the default margins the right side is cut off and the bottom margin is too long.

I tried to set the margins manually, but because they refer to portrait mode, new values where not accepted (physical limitation of the printer).

There was no other way than to calculate the rotated rect alone and to use QPrinter.setFullPage(true).