Low Login Screen Resolution

Hi

I run my mid-2013 13" Mac Book Pro Retina running OS X Yosemite (10.10.4) in the highest possible resolution ("More Space"). I have recently noticed that the login screen on first boot up is at the default resolution which looks very low resolution compared to the normal desktop. When I login, the screen flickers a couple of times and the screen resolution is set correctly (to "more space"). If I log out the login screen is at high resolution, so the problem is only on the first boot up.

It would appear that OS X has only recently started doing this as it always booted to a high resolution login screen.

Are there any known fixes to this and is this a known bug in the latest update (10.10.4)?

Mark