If we drag-n-drop from some regions of middle left or middle right hint of splitpane with horizontal splits then position of splitpane divider will be changed, but size of splitpane won't be changed.
 
Steps to reproduce:
0. Open empty document in scene builder.
1. Drag-n-drop horizontal splitpane to designed scene.
2. Try to resize by middle left or middle right hint. In some point of hint you can't change size of control, position of splitpane divider will be changed.