To reproduce:
- load an image node into the data storage and select it in the segmentation plugin in the first combo box
- create a new segmentation and select it in the segmentation plugin in the second combo box
- load a new image node (not a segmentation) into the data storage and the selection of the segmentation node is lost
This happens because of the "NodeAdded" function: Here the index of the segmentation combo box is always set to the newly added node. Since the segmentation combo box does not acceppt non-segmentation images, the newly added node will not be found as an entry of the segmentation combo box and thus the combo box index is set to -1.