It's because you have a trace amount of charge in the battery now, which is depleted each time you turn the key and attempt to engage the ignition/starting process, but it then recoups slightly after a moment, which then allows the interior lights & locks to function somewhat. When your battery was dead before and nothing worked at all, it was because there was truly nothing in the battery.
I had the exact same scenario in my previous car, and it was a dead battery. Also, fully bringing a car battery to absolute zero is very hard on it, so it's likely that when your battery was dead before, it was the last nail in the coffin regardless of your attempt to recharge it afterward.
Last edited by ZeGerman; 11-15-2012 at 03:48 PM.