This is by design
https://meta.discourse.org/t/a-thought-on-css-and-customization-in-general-optional-disabling-on-the-admin-console/10126/6?u=robmc
To avoid the potential of customisations affecting your ability to access admin pages, this header area is different.
If you navigate away from it, it does not necessarily reload (it would slow the whole site to do this every time). Since this ONLY affects those with Admin access, I believe it is a small sacrifice to need to refresh if you need to reload the header in exchange for being able to rely on accessing your admin console.