I have been experiencing this bug for a long time now so thought it's about time I reported it here. I have Windows 7 32-bit(official RTM, clean install) only 1 account on it which of course is Admin.
Sometimes when I press the Windows button + l to lock the screen and come back after a few minutes, enter the password but Windows 7 reports it as wrong password all the time. I have had the same password for 3 years so I know for sure I entered it correctly all in lower case.
Also, if I deliberately try to enter a wrong password when my normal one doesn't work, I get the white round circle indicating that its being processed. Then after like 3 minutes, Windows 7 reports it as being the wrong password (the correct behaviour from Windows 7 would have been to reject the the wrong password immediately).
So I have to do a manual shutdown as it's the option left. I have tried to reinstall Windows 7 many times but this problem just keeps happening randomly. Most of the time though it doesn't happen.
I have a Dell M1530 laptop, Windows 7 32-bit RTM official. All updates as of 22nd Feb 2010.