QT tabs don't display ampersand normally as they are used as shortcuts (http://doc.qt.io/qt-4.8/qtabwidget.html#addTab). This was issued here : https://bugs.kde.org/show_bug.cgi?id=382512.
Pressing alt would enable to use the letter following the ampersand as a shortcut. If a user use this character in a tab title he might be confused not to see it displayed
By doubling the ampersands in the tab titles, the issue is fixed (at the cost of not being able to make shortcut when we understand the QT system)