popular-labels heatmap style inconsistent for global/space labels

The look of the popular-labels macro is different depending of the "spaceKey" parameter. If it is present, then the names are sorted alphabetically; if not, they are sorted by popularity.

My expectation is that the macro should display the labels by popularity, regardless whether the spaceKey parameter is present or not.

See also http://www.schirmacher.de/pages/viewpage.action?pageId=3801089&focusedCommentId=15073282&#comment-15073282

Same behaviour is also observed when viewing all labels for a space or for the whole site in the label screens.