In QmitkMultiLabelSegmentationView.cpp line 943 (2016.11 release branch) Modified() is called on the BaseData of a DataNode without checking against nullptr in advance.

The code is within QmitkMultiLabelSegmentationView::OnPreferencesChanged() so it is a bit more tricky to reproduce.
Anyways checking against a DataNode with a BaseData == nullptr is necessary here.
Looking onto it with the debugger I saw that the data node causing the seg fault was an interpolation data node. Seems as is the interpolation node doesn't contain a BaseData.

I will create a pull request as trivial bugfix and need a bug number for this.
;) keep up the great work!
Much appreciated!
Ingmar