Divarea - changing tabs and applying styles throws JS error

[Jakub Ś]

Steps to reproduce

1. Open two tabs in Chrome or Opera
2. Open divarea sample and clear editor contents.
3. Type text, select Big from styles dropdown, type more text, select Small and type more text
4. Click on another tab, click on tab with editor and select e.g. Typewriter style from dropdown.

Expected result

No JS error is thrown

Actual result

JS error is thrown:
Code: selection.js
Line: 1921
Message: Uncaught IndexSizeError: Failed to execute 'setStart' on 'Range': The offset 22 is larger than or equal to the node's length (15).

Code: style.js
Line: 331
Message: Uncaught TypeError: Cannot read property 'elements' of null

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