When I have an open project and selects "Add New" -> "C/C+" -> "C/C+ Header File" qtcreator hangs. 

I have debuged this and it is hanging in source file src/plugins/[projectexplorer/projectnodes.cpp |https://github.com/qt-creator/qt-creator/tree/master/src/plugins/projectexplorer]at line 351-352. That is, it is stuck in:
...
while ((!fi.exists() || !fi.isDir()) && !fi.isRoot())
    fi.setFile(fi.absolutePath());
...
The context is that fi.fileName() == fi.absolutePath() (both are empty strings), and thus qtcreator is stuck in the while loop. Adding extra condition to the while loop seems to fix the problem (at least for me):
+    while ((!fi.exists() || !fi.isDir()) && !fi.isRoot() &&
+           (fi.fileName() != fi.absolutePath()))
+      fi.setFile(fi.absolutePath());
 
Hope this helps developing the tool