extractContents returns incorrect result when multiple nodes are selected.

[Jakub Ś]

Steps to reproduce

1. Put attached sample into ckeditor/samples folder and open it
2. Apply same styles and selections as in attached video:
   • This is some [sample text.] - apply yellow marker
   • This is [some sample text.] - apply underline
   • [This is some sample text.] - press Print Extract Contents button

Expected result

This is <u>some <span class="marker"><strong>sample text</strong>.</span></u>

Actual result

This is <u><span class="marker">.<strong>sample text</strong></span>some </u>

The text content in Document Fragment is "This is .sample textsome "

Other details (browser, OS, CKEditor version, installed plugins)

Problem can only be reproduced in Chrome (Win and Mac) starting from CKEditor 4.5.0.