This issue has 2 related bugs in OTSU tool.
Workflow:

1. Load 3D image and open Otsu tool.
2. Change "Number of Regions" to 4.
3. Click Preview -> 4 objects are added to QmitkSimpleLabelSetListWidget for Preview. (See by selecting "Transfer selected labels")
4. Change "Number of Regions" to 3.
5. Again, Click Preview -> Still, 4 objects are unchanged to QmitkSimpleLabelSetListWidget for Preview. [Bug 1]
6. Select "object-3" (the ghost object) and Click "Confirm Segmentation" -> The "object-3" is added to QTableWidget after Confirmation. [Bug 2]