This is a bug that occurs in the VisualTool that I didn't manage to isolate outside of the VT context. I am adding at the end of the description the few steps required to reproduce it by using the visual tool.
We are observing that the content of some Tabs are not rendered (although the content is there and added to the containment tree).

This happens when the mouse pointer goes upper than the Tabs location, the description looks crazy but it is a way to reproduce the problem. As soon as the mouse pointer goes once upper than the tabs and that you click on the tabs, the content is not rendered.
Strangely enough, to have the Tabs content to be rendered you need to move the mouse upper the tabs again....
Yes, I agree the way to reproduce it is very strange. You should better follow these steps to reproduce. These are observed both on Mac and Windows using Control SCRUM : 364

Steps:
1) Download the VT (on Mac : http://athudson.us.oracle.com:8080/hudson/job/AuthoringTool-nightly/378/label=master/artifact/AuthoringTool/dist/VisualTool-1.0.zip on Windows :http://athudson.us.oracle.com:8080/hudson/job/AuthoringTool-nightly/378/label=windows-i586/artifact/AuthoringTool/dist/VisualTool-1.0.zip

2) Unzip it.

3) Launch it: VisualTool/bin/tool.sh or VisualTool\bin\tool.bat

4) Click on "Open Existing..." Select the attached test.fxml file.

5) Select the SplitPane located in the middle of the Stage (white Rectangle). Some information is now displayed in the Tabs, on the right.

6) Now click on the tabs on the right by making sure not to have the mouse pointer to go upper the tabs. All should go fine. The Tabs are showing some content.

7) Move the mouse upper the Tabs, click again on the tabs, you will observe the problem. To have the tabs content to be displayed, move the mouse upper again.