- Please see the attached test case.
- The Region(StackPane in this case) has initial default values all 0.0 but Group has -1.0 for maxX ,maxY, w,h

See the following

Region Bounding box : BoundingBox [minX:0.0, minY:0.0, minZ:0.0, width:0.0, height:0.0, depth:0.0, maxX:0.0, maxY:0.0, maxZ:0.0]
Group Bounding box : BoundingBox [minX:0.0, minY:0.0, minZ:0.0, width:-1.0, height:-1.0, depth:0.0, maxX:-1.0, maxY:-1.0, maxZ:0.0]