Until Qt 4.4.3 QString could be used without instantiating Q(Core)Application resp. without using QTextCodec::setCodecForLocale().
With Qt 4.7 (4.5 4.6 ?) this is no longer provided (see http://bugreports.qt.nokia.com/browse/QTBUG-13508?focusedCommentId=131579).

Therefore QString, QFile, QDir, ... (classes that depends on QString and don't need event handling) can no longer be used in library code,
because a library cannot set the applications locale settings nor can it rely on the application to instantiate a Q(Core)Application.

As a consequence, libraries using QString and developed with Qt <= 4.4.3 cannot be migrated to Qt 4.7 (4.5 4.6 ?),
if used on non-ASCII-platform like e.g. Suse Linux 10+ (UTF-8) !

This is getting worse, since Qt 4.4 is not maintained any more.
See attached test program.