Cannot unlock laptop after closing lid

If I close my laptop lid without first manually locking the screen, the screensaver seems to take a screen capture and then blank the screen. When I reopen the laptop and resume, this screen capture is displayed full screen and blocks the password entry dialogue, which is both invisible and does not have keyboard focus. The only way to log back in is to switch to a text console, log in and kill the screen saver (which also kills the lock screen), log out of the text console and switch back to the graphics VT.