PaintLine not correctly drawn if out of pad

I have a TLine, but it is not correctly drawn if one of the coordinates is out of the pad, ie, it is drawn as a vertical line, but it should be oblique. The bottom coordinate is changed somehow when drawing.

See attached script and data file, which is run through
root -l opg2root.cpp+(\"tests.opg\") -b -q -n

See then tests/s10_hYX.png, the green vertical line, (second screenshot).

If I uncomment line 1396, then the arrow is drawn correctly (first screenshot).