Subscript and superscript cannot be removed after applying on a text on Chrome 39

Steps to reproduce:
1. Open Chrome v.39
2. Create a new page
3. Enter some text and then click twice subscript button from WYSIWYG bar.

When you click for the 1st time the subscript/superscript button, the style is applied.
When you click again on it in order to remove the style, nothing happens.