MBP screen turns off after a few seconds after waking

Whenever I open my MBP after closing it to put it into sleep mode, it wakes up, displays the login screen and then the screen dims again. I have to push one of the brightness keys to turn the screen on again. I don't think it's asleep because I can type in my password and then turn the screen back on again and it's logged in, and the keyboard lights stay lit. This only happens if I put it to sleep when closing my MBP. If I leave it open and let it go to sleep while it's open, this does not happen.

This is a new MBP, I got it in June. It hasn't always done this and I started noticing it after I updated to OS X Lion.

While this isn't making my MBP unusable, it is annoying to do every time I open my MBP. All help is appreciated!