If the MxN Multi Widget is used and a render window is set to "individual / local selection" (i.e. the "Select all nodes" checkbox in the "Data" drop down is unchecked), newly added nodes will not be added to the current selection of that render window.
This is an issue for new child nodes, such as newly added segmentation nodes, created polygon models etc.
To reproduce:

• open MITK, load an image
• close the Standard Display, open the MxN Display
• uncheck the "Data -> Select all nodes" checkbox
• open the Segmentation view, create a new segmentation node
• draw in the render window
• see how the finished segmentation mask is not drawn
  • check the selected nodes in "Data" and see that the segmentation node is not available