When you work around it in your code and don't tell me what went wrong I can't fix it in the lib.
The printer sent with QPrintPreviewDialog::paintRequested(), returns QPaintEngine::Picture for paintEngine()->type().

This was the workaround I used:
Qt Code: 
  1. void PlotTextLabel::draw( QPainter *painter,
  2.                             const QwtScaleMap &xMap, const QwtScaleMap &yMap,
  3.                             const QRectF &canvasRect ) const
  4. {
  5.     if (painter->paintEngine()->type() == QPaintEngine::Picture) {
  6.         const int m = margin();
  7.  
  8.         const QRectF rect = textRect( canvasRect.adjusted( m, m, -m, -m ),
  9.             text().textSize( painter->font() ) );
  10.  
  11.         text().draw(painter, rect);
  12.     } else {
  13.         QwtPlotTextLabel::draw(painter, xMap, yMap, canvasRect);
  14.     }
  15. }
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This would have worked, but may have some side-effects.
Qt Code: 
  1. bool QwtPainter::isAligning( QPainter *painter )
  2. {
  3.     if ( painter && painter->isActive() )
  4.     {
  5.         switch ( painter->paintEngine()->type() )
  6.         {
  7.             case QPaintEngine::Pdf:
  8.             case QPaintEngine::SVG:
  9.             case QPaintEngine::Picture: // <- Here
  10.                 return false;
  11.  
  12.             default:;
  13.         }
  14.  
  15.         const QTransform tr = painter->transform();
  16.         if ( tr.isRotating() || tr.isScaling() )
  17.         {
  18.             return false;
  19.         }
  20.     }
  21.  
  22.     return true;
  23. }
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