Humm here's an awkward one - I occasionally get output like:

tests/cpp_unit/Simulation/MAUSSteppingActionTest.cpp:122: Failure          
Value of: 9.                                                               
  Actual: 9                                                                
Expected: out["momentum"]["x"].asDouble()                                  
Which is: 3.9693107475943875e+114                                          
tests/cpp_unit/Simulation/MAUSSteppingActionTest.cpp:123: Failure          
Value of: 18.                                                              
  Actual: 18                                                               
Expected: out["momentum"]["y"].asDouble()                                  
Which is: 7.938621495188775e+114                                           
tests/cpp_unit/Simulation/MAUSSteppingActionTest.cpp:124: Failure          
Value of: 27.                                                              
  Actual: 27                                                               
Expected: out["momentum"]["z"].asDouble()                                  
Which is: 1.1907932242783163e+115                                          
tests/cpp_unit/Simulation/MAUSSteppingActionTest.cpp:126: Failure          
Value of: 9.                                                               
  Actual: 9                                                                
Expected: out["energy"].asDouble()                                         
Which is: 8.753015450537953e+227                                           

from the unit tests. Seems to occur only occasionally - which probably means something isn't being allocated that should be. (Check with valgrind?)