editor remove block style, when trying to change style inside a block

[noam]

1. got to full demo: ​http://ckeditor.com/demo#full.
2. select some text, and color it.
3. set the cursor to the middle of the colored text (select nothing)
4. change the font color, in order to start typing in the new color.

Actual result: Old color is removed from the block. The span is removed

Expected Results: Old color remains, and new text is written in new color.

Happens to other styles too.

[Jakub Ś]

DUP of #8934.