Building the current master with the Clang compiler gives a build error in the QmitkServiceListWidget:

/Volumes/Macintosh_HD_2/projects/mitk/Bugsquashing/MITK/Modules/Qmitk/./QmitkServiceListWidget.h:116:102: error: non-const lvalue reference to type 'std::string'

  (aka 'basic_string<char>') cannot bind to a temporary of type 'std::string'
void Initialize(const std::string& namingProperty = static_cast< std::string >(""), std::string& filter = static_cast< std::string >(""))
                                                                                                 ^        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

There simply the const declaration for the lvalue is missing which is need when binding a temporary to a reference.