I remember having a lot of problems with this years ago, when I was in the horse breeding business and someone on another server wanted to reserve specific horses to pick up later. I got so worn out having to arrange meet ups to open the pens for folks because mailed keys didn't work when they got there, I finally just stopped offering to reserve the animals. So, either that has been a thing for a very long time, or it is a 'returning' bug if it was fixed in the past.
I recently moved to a new server and also found various keys to things like magic chests no longer worked as well, eventually all got sorted out but mostly I just replaced locks and keys where I could. So like the tent lock problem, it seems to affect a lot of different things when it comes to crossing servers with anything involving locks and keys.