SplitPane : issue with position setting

Launch the attached test case.
Using the first text field, set the first divider position to 0.2 : the divider move correctly.
Now, using the second text field, set the 2nd divider position to 0.5 : the 2nd divider does not move. This is expected, since the Button cannot grow. But the 1st divider is moving : this is not expected.