What are these tonal markings called?
This a well-known issue to do with the rendering of contour tones in certain computer fonts. The Wikipedia article for tone letter states that:


  The contour-tone letters are composed as sequences


In the "Modifier Tone Letters" block in the Unicode standard (A700-A71F in Unicode 7.0), only the level tone letters are provided. Hence any non-level tone letter is created by "smart rendering" capabilities within the program and within the font; it is usually classed as a type of ligature. However, many (or most?) browsers cannot handle them, or only provide some of the ligatures.