Wysiwig editor not opening

I have a similar problem now with WP 3.9. I have a 2nd metabox wysiwyg-field on the post-new.php edit-page and now I cannot use the “Distraction free writing” button (the maximize function of the wysiwyg-field) any longer. If I click on the max-button on my own wysiwyg-metabox-field only the main wysiwyg-field is maximised together with the blogentry-title field.

There has been the same issue 2-3 years ago with a new WP version. Also when I clicked on the red Save-button in fullscreen mode the entered text has not been saved. I don’t know if this is again an issue, but the maximize button is.

Thanks for help!