I am running Ubuntu 14.04 (64 bit). In my previous Ubuntu, which was 12.04, when the screen was locked and the monitor went blank, I just typed the password and hit enter. Even though everything looked blank, it worked in the background and unlocked the screen. However, in 14.04, when I directly type the password from the lock screen (with the monitor out), often times it misses the first character and obviously tells me that the password is wrong. So now I have to type the first character, wait a bit for the screen to come up and see if it was registered, and then type the rest of the password depending on that. Not that big of an issue, but for someone who locks the screen almost every time he leaves the PC, it's a little annoying.
Any way to fix this?
Are you using a wireless keyboard? I think this has something to do with the keyboard (and/or keyboard driver) "sleeping" if it is not used for few minutes. This only seems to occur on my first attempt at entering my password, or if I haven't hit any keys for awhile.
I would think this is most likely an issue with my keyboard. It is a cheap wireless keyboard by Logitech. It probably has some built-in sleep mode to conserve battery. Higher-end keyboards may have built-in "turn on and send first entry" process. I don't know. Just what I have observed.
Maybe try getting in the habit of waking your machine via keystroke? (Hit 'Enter' to wake instead of moving your mouse...)