Oh.. I figured it out. That's just a simple unit conversion error. I used millimeter instead of pixel... >>> # Python >>> __editor.mmMarginLeft() 20 >>> __editor.pxMarginLeft() 110 >>> __editor.mmMarginLeft() == __editor.pxMarginLeft() False Now it's solved! THANKS a lot! [image: 3c6e7a83-38e3-418d-a776-ec4e984bfd1f.png]

@tapsbrighton This is a better solution rather than append: insertPlainText("\n");

Terribly sorry, but it turned out to be my fault all along. The line responsible was: textDoc.setDocumentMargin(0); in the sizeHint() method.