Do you get the same result with the following code?

<a title=" Forums" href="/new/forums"><span class="icon icon-edit"></span> Forums</a>

Then it showed correctly

The icon class has a width: 28px; making the a container to be small width where the text has to be displayed vertically. You will have to change your markup as advised.

Try your markup with icon-edit only without icon.

@Quy is this a Core Issue?

Set to "closed" on behalf of @Quy by The JTracker Application at issues.joomla.org/joomla-cms/20581

Closing as not a core issue.

the issue is on the menu, so also core. You can't add now a icon on the menu item

Set to "open" on behalf of @Quy by The JTracker Application at issues.joomla.org/joomla-cms/20581

Was this possible in previous versions? I had to create a custom css .auto-width {width:auto;} as follows icon icon-edit auto-width to make it work.

This is coming from Bootstrap and is expected. See documentation http://getbootstrap.com/2.3.2/base-css.html#icons.

The markup posted by @Quy is correct. If there's demand, 'Icon Class' option could be added to create correct markup for icons. Or you can use additional class to set the width as shown above.

Set to "closed" on behalf of @franz-wohlkoenig by The JTracker Application at issues.joomla.org/joomla-cms/20581

closed as stated above.