Changing PB battery with backup

So I used to be able to change my PB 15" battery while it was still on. I think the backup battery would last 3 minutes or something. But today, as soon as I took the battery out, it shut down. I have no idea what I've done differently but it is extremely annoying. Any ideas?

It was asleep when I did it. But it wouldn't wake back up. That's cause it turned off completely. I have since tried it 3 more times and it keeps shutting off. Now, aside from it being annoying, is it causing damage?

EDIT: I stand corrected. My PB isn't going to sleep properly when I shut the lid. That's why it is turning off when I take out the battery. Now that's an entirely different problem.