I got the same kind of issue a few minutes ago, I did not test all configurations. It occurred at the Vista login prompt.
- Sony Vaio VGN-CS11S
- Used keyboard from the laptop (not external keyboard)
- Laptop on battery (not connected to sector)
- At Vista login prompt, I pressed the "power" button accidentally as the screen was darkened.
- After some time, the laptop becomes sleepy.
- I boot up using the "power" button, till the login prompt.
- Then, my password failed to be recognized, by pressing letters one after the other, the combination Shift+L was not providing any letter while the combination Shift+G seemed to add the capital G letter as expected.
- Using Caps Lock, I was able to show a bullet after pressing the L, but I can't say if it was really a capital L: the password was not valid even after entered the letters properly.
I forced a hard power off by pressing the "power" button during 4 seconds. The reboot fixed the bug.
I imagine the issue is either related to the keyboard or to its driver, or to a Windows middleware; the application layer seems not to be in cause since the failure occured on both IE and the login prompt (Windows-specific).
Hope it could help,