When I run CoqIDE under KDE (specifically Kubuntu) all the symbols are wrong and it crashes when I open the query window. My solution to this problem was to reconfigure how KDE handles GTK applications (such as CoqIDE).
In Kubuntu I go to System Settings -> Appearance -> GTK styles and fonts. Under GTK styles I select Use another style and chose the Raleigh style. This solve the problem for me. Someone with a more detailed understanding of what is wrong and how to fix it is welcome to improve this document.