Aww I think Tyson might just still be adjusting to your family. It can take a rescued pup awhile to really come to the realization he is in his forever home.
Kind of funny thing about Magoo he recently started humping other dogs in play, I thought this was a little wierd for him to start doing out of the blue. But a gal who works for rescue told me it was a good sign it meant that he was gaining his confidence back, kind of funny. Now we always joke about Magoos low self esteem but really it is true. After a year his esteem is improving and he is gaining alot of confidence with us. That may be the same with Tyson. Or you may just have a clinger =)