Note: this is an issue I fail to reproduce in a smaller test ; it does however occur all the time in an application I am currently porting from Swing to FX 2.
I will attach the part of the code that is currently causing trouble.

At FX app thread, I create a tab pane and a bunch of tabs initilized empty by defaut. Each tab is linkedto an object which will generate charts to be displayed on that tab whenever the user click on it the 1st time.
Then I initialize the creation of the charts of the very 1st tab of the list as it will be always visible to the user by default.

If I do the tab initialization in the same sequence of code, the arrow button of the tab view does not pop up and remains barely visible (and clickable) on screen (see first screenshot). It stays popped down all the time even when resizing the window (see second screenshot).

On the other hand, if I move the chart initialization into a later call using Platform.invokeLater(), the arrow button appears popped up.

In the code, the problem occurs if line 117 is uncommented and line 126 is commented.