Sorry, Been a bit busy. In the server console the list is not cut off. Just checked 13w07a and the bug still appears, I would only assume that the bug has occurred in previous releases however, I wont document it until I can prove it.
Can comfirm. Album with data values. http://imgur.com/a/kGNtQ
How many times did you repeat the process, When I notice this it was on multiplayer if that helps.
I believe entity (Mob) disappear in unloaded chunks.
Comfirmed in BDoubleO100's video. Link provided.
http://www.youtube.com/watch?v=dCFAD0tAMxY&list=UUlu2e7S8atp6tG2galK9hgg&feature=player_detailpage#t=1202s
You can't /tp to different Dimensions
Just checked with version 13w24a, seems they have fixed it. Bug no longer exist.