When updating a Tab Display the TinyMCE toolbar does not display for the 2nd and subsequent tabs. A whirling arc indicating that the browser is trying to load something appears near the text windows for each of the tabs that the toolbar is not displaying.
The problem occurs on various devices - Mac, PC, iPad - and a number of browsers - Safari, Firefox, Internet Explorer, Chrome. When using Safari if I 'Remove all website data' the problem is solved, but I have to do that each time I wish to edit the tab display. I have found no similar solution when using Firefox, Internet Explorer or Chrome.
The problem only occurred since upgrading from Moodle 2.3 to 2.4, and doesn't happen when editing anything else but tab display.