strange login page

For some days now, I have a strange login page: the regular lay-out is missing, although username and password are shown.
When I click login, sometimes I do get logged in rightaway, and sometimes I see the regular login page, but with a white field with a stipe of red on the left of the white field. I do get logged in after clicking on login.

There may be no real problem, but I just want to make sure that it’s not an indication of some other problem.

I made a printscreen (removed the username though): https://dl.dropboxusercontent.com/u/19259857/Wordpress-login.pdf

Could anyone help me out please?