I am guessing that the Trackables is being taken as swag. I had two Geo Cachers who where teachers come to my cache and take a travel bug. They did not list it in their hands even after I emailed them on how to do it. After 2 more weeks went by had to place it as missing. Things happen and you move on.
Can you go back to a house and grab a travel Bug....I would say sometimes it is OK..What if you put a Travel Bug in a cache and after looking at the bugs you moved you find the same bug in the same place six months later. I will go back there and move it to a more active cache. Bottom Line travel Bugs were meet to travel.