So I had to upload an SVG flowchart which looked great on my computer. However, when accessed from the server, certain text elements were displayed as large black boxes. This was happening only with converted PNGs of the SVG as the SVG itself rendered just fine. I initially thought that this was some kinda font issue. But apparently not. This happens because Inkscape's SVGs are not always valid and in this case, uses something called a flowRoot element which is not valid SVG.