When playing Grandia (although the same happens in Tales of Destiny), all text shown on screen overlaps the previous sentence, meaning short sentences still show part of the previous text.
If the conversation finishes, the next one will start with the last one on screen, overwriting again
i had this problem with two games i tried. one was grandia like you said and the other was azure dreams. this only happens when in opengl.
software mode gets rid of the problems however it can also be played on opengl without the text problem by playing around with the video setting. i have frame texture and offscreen drawing enabled and the texts play normally in opengl.