In the data selection of each render window, nodes can be selected (i.e. if they are shown at all) and their visibility can also be toggled. As such, a node can be selected but at the same time not visible. When at least one render window is in the synchronised mode, with Select All turned on, and a data node is in the selection but turned invisible, adding a new render window will turn any invisible nodes visible again.

This happens because in QmitkSynchronizedNodeSelectionWidget::ReviseSynchronizedSelectionChanged() all nodes that weren't previously selected, but are now in the selection, are turned visible. When a new window is created and the selection is set, there are no nodes in the previous selection, so everything is turned visible by default.

Steps to reproduce:

1. Open workbench
2. Open MxN view
3. Load an image
4. In the render window Data menu, turn the image invisible (synchronization and Select All should be kept active)
5. Change the layout, so that at least one more window is shown
6. -> The image is turned visible again