I'm running KDE on a Gentoo system. When using liberation-mono version 2.0, or the inconsolata font (and possibly other monospace fonts) in konsole, the spacing is wrong and leads to display errors. (I'm attaching screenshots of pressing a sequence of d's that moves the curser too far out). This does not happen in other kde applications such as kate. In the corresponding KDE Upstream bug we tracked the issue down to QT returning different widths for different characters:
https://bugs.kde.org/show_bug.cgi?id=305555