Repository HTTP configuration not available in Safari

In the edit screen for a proxy repository the http configuration sections are not displayed when viewed in Safari. Works fine in Firefox

This issue isn't just affecting the HTTP Configuration section, all the subheadings on the new Repository form page are now hidden. See screenshot below:

It also affects other pages with similar elements. e.g.

 What's more, after the ExtJS upgrade, the style of the subheadings on all browsers is off. They are supposed to be larger than the form fields as shown in the Chrome screenshot below:

But after the upgrade, the structure of the DOM nodes that ExtJS generates was modified and the custom CSS style rule for subheadings is no longer matching. Therefore the subheadings look like all the other text on that page as can be seen on Chrome below: