Old Dog, New Tricks

How does this happen?  After 11 years, Drexyl has decided to change his ways. He's been sleeping in our bed since he's a pup.  The past 3 nights he's gone missing in the middle of the night.  I get up to take care of someone's wet diaper, missing paci, fill in the blank -- and he's gone.  I run all over the house and eventually find him in Jackson's bed.  Jackson, whose room is completely clear of toys, stuffed everything, rugs, etc. -- and whose door is kept shut with an air filter running 24/7 for his asthma -- now has an 11 year old dog sneaking into his room at night.  Is it any wonder?