One of the most reliable "bugs" we met regularly is what we call the "Umlaut" bug. Often we notice cases in our database which are displayed incorrectly. Namely Polish and/or German characters are regularly screwed up somewhere. Corrupt here means that it is displayed as a black square with a white question mark or a simple empty rectangle. The test pattern to look for broken text is effective at all test levels, be it it the UI or even at a lower level such as Web Service responses.