In QTabWidget if the tab label contains &, it is used as an accelerator (shortcut key). By simply replacing QTabWidget with a KTabWidget this break, and the & will appear as it is and a new accelerator is chosen by the framework. This is a regression to KDE3 (and of course makes KTabWidget to not be a compatible replacement for QTabWidget).
Here using: Qt: 4.5.0 + qt-copy-patches-936035 KDE: 4.2.68 (KDE 4.2.68 (KDE 4.3 >= 20090327)) kdelibs svn rev. 946159 / kdebase svn rev. 946160 on ArchLinux i686 - Kernel 2.6.28.8 I can't reproduce this bug. Closing as WORKSFORME