Post: Image viewed in overlay causes user to press browser "Back" button 2 times instead of once

How to reproduce:
1. Create a topic and add a picture there with [img] bb code
2. Open the topic, click the image -> Image is opened in overlay
3. Close image view by pressing the X button
4. Press browser "Back" button

AR: User has to press "Back" 2 times before previous page will be opened
ER: User presses "Back" button one time and the previous page is opened

Note:

• Reproduced for any browser (I tried Chrome, FF)
• On each click URLs are changed, but user stays on the same page in the same state