l noticed that the underscores disappear or become cut when increasing the font size to specific values.  When putting solely underscores in a line, they are invisible. When a space or some letter is added to the line, the underscores are slightly visible. l use sub-pixel-geometry, thus that the slightly visible underscore is green means it's the top part and the lower pixels (or whatsoever) are cut. line 934: 3 underscores, 1 space line 935: 3 underscores