http://qt-project.org/doc/qt-4.8/qpainter.html#drawText-10 says:

"Draws the given text within the provided rectangle."

The word "within" is slightly misleading. The rectangle is merely used as the basis for positioning the text, but no attempt is made to put the text "within" the rectangle if it does not fit into it.

The sentence concerning alignment is incomplete:

"Note: The y-coordinate of rectangle is used as the top of the font."

This is only true for AlignTop, not for other alignments.