When you add tab, if pref width is set previously, added tab will not be shown.

On movie: on the left, pref width is set, and tab added; on the right : just added a tab. You can see, that on the left, tab was not shown.

To reproduce : set pref width, and add a tab.

Affected tests:
ControlsAutomatedTestSuite/javafx/scene/control/test/tabpane/NewTabPaneTest/visualFocusScreenshotTest