L.,
I think there are things that just "happen" and aren't normal but not anything to be worried about either. When both my daughters were born, my son reverted and started to wear diapers or pull ups, but he hid it. We would know that he was wearing them under his clothes or that he had them hidden under his bed and he would wear them for an hour or so and then change before bed. I don't know what was going on and I was a little worried, but we tried to just ignore it and let him do his thing. Well, he will be 13 in 2 weeks and he is completely normal, well as normal as a 13 year old boy can be, ha ha. I am glad that we never made a big deal about it. Who knows why he did it, but he got over it and doesn't remember (or so he tells me that) and all is good. I think with all the things we need to deal with when they are teenagers, we should let go of some of the crazy stuff now because it will seem like nothing later on (like when they stink really bad and are getting hair in other places, etc.)
I hope this helps you to not worry!!
K.