login password incorrect when unlocking after Window-L

When I'm away from the my machine, I usually Windows-L to lock the keyboard.

If I return in a short period, I can unlock the userid with no problem. However if I'm away a while say 20 mins then Windows 7 says the password is incorrect

Only way to get round this is to choose switch user to display all userids, then choose the same userid and then the password works.

Thought I was typing the password wrong, but I have carefully checked what I type each time by being very deliberate in my choice of the characters entered so I know it is correct. If it was to be validly wrong in the first instance, then after using Switch User it should still be wrong, but it not because it works.

I've tried searching Microsoft.com but haven't found any hit. Has anyone else experienced this and found a fix?

I'm running Windows 7 Ultimate on an HP Mininote machine (with an Atom processor), offered for purchase at a 2009 Microsoft TechEd, so the Windows install should be good (would MS supply/be involved with a dud installation?).

 

Re: Wondering if the keyboard is asleep..

Yes, I see stars as I type. And I even double-check state of CAPS LOCK, making sure it's off. If it was on, the password would be wrong & entering the password after Switch Users done would also fail (but it doesn't).