Minor issue regarding login in to portal

[#1]

I no longer set Auto-login and haven't done for some time as it seems to periodically just turn off.
For some time when I refresh a page (say the VMBU) I get the screen below which tells me:
"Invalid username or password. Please try again"
Simply clicking Login logs me in as normal.
As I say, not a major issue but wonder why I do continuously get such a message even after reboots?

[#2]

I believe it's cookie based, do you set your browser to remove all cookies on a restart? That could be doing it.

[#3]

Sorry, Matt, just noticed your reply.
My browser never removes cookies on a restart.
It isalso an intermittent issue as there are occasions where i don't get the above message.

[#4]

I sometimes get dropped by Auto-login too. Other sites usually log me out at the same time -- Google, Facebook, etc.  I blame it on an automatic update of my browser deleting cookies. It's no biggee....
Best wishes
Chris