KDE 4.14.3 Please see the attached screenshot. Reproducible: Sometimes Steps to Reproduce: This happens sporadically and in a handful of apps; it's hard to reproduce. For example, when it happened in LibreOffice, resizing the window, which changed the font sizes, caused the missing / blocked out characters to appear.
Created attachment 91655 [details] screenshot of character rendering issue
Please report this issue to the developers of your video drivers.