If this helps anybody, I just experienced this for the first time today, but in OS2008. I locked the screen seconds after disconnecting an audio jack and a minute later tried to unlock it but got no response from the D-pad centre button. I managed to get the screen to unlock by popping the camera out. Naturally this launched the camera application, but it seems better than waiting or taking the battery out.

Does anybody know of a bug report relating to this? It does seem software related.