Doubled title suffix in admin (backend) pages - Magento 1.9

Question

A client needs to add Title Suffix to show in all Magento administration pages. So I added it in System -> Configuration -> General -> Design -> Title Suffix and when I enter some text, this text shows twice. For example, if I enter | My page, it shows:

Configuration / System / Magento Admin | My page | My page.

Is this Magento bug?