Honestly, it sounds like he just misses you when you are gone. Thats probably why he has "setbacks"...he misses his mom and dad, just like a child would. And expresses his anxiety by rebelling, once again, just as a child would. I'm sure he would appreciate it if you took him with you on your travels, if at all possible.
When your friend cares for him while you are away, does she stay in your house with him, just come visit to feed/water/play with him, or bring him to stay with her?
Welcome to YorkieTalk Chrisann and Cinnamon!
