Static const member value not available (at runtime) - code works fine under VS2010 but porting to Qt5 causes a crash

[Dolphin]

Developed under Qt 4.8 last year using Visual Studio 2010 and have had the code working for months. Moved to Qt5 this year and also started using Qt Creator (QML/QtQuick 2). The code contains a global class (long story!) which has a QString and an int as member variables. When I call a method that should update the QString and the int - the int updates fine but the QString assignment causes a crash. Looking at the "watch" window it says <Static const member value not available>. (FWIW* The QString is initialised fine in the constructor);

There is a lot of code so I am not including it, I am hoping for some insight to narrow down the search then post snippets if necessary.

Any clues?