Yes it's true, my 2 yr. old will strip down- pjs, diaper & all- and go au naturel every chance she gets! During the day she's more conservative and usually just takes her pants off and leaves her diaper on, but at nap & bedtime all bets are off.
We lay her down to sleep (fully clothed) and shortly after we leave the room... she frees herself. We tried at one point even putting her pjs on backward so she didn't have easy access to the zipper. That worked for a little while but then she started pulling Houdini stunts and wiggling out of them.
So now, she's back to wearing her pjs frontward and still takes them off whenever possible. We have gone back in to check on her before heading to bed ourselves and there she lay, naked as the day she was born. This is completely adorable to see, and gives my hubby and I a good laugh while we redress her, but it's not ideal when she isn't potty trained yet! So next step.... potty training here we come!!