So I just got my cat the other day, and I play on two sims. My home sim, and a role-play sim owned by my parentals.
Anyway, I went to show her to daddy and my brother. She was kind of posed weird so I dropped her to set her down, then she poofed. I relogged, checked my inventory, and she was nowhere to be found. Thankfully my brother searched my name in the object.. searcher.. thing. and he found her, over 4000 meters in the sim next to us? We were on a skypad 3000 meters in the air. So, I don't really now how she got there, but that was a long way to travel for a little kitty. :<
I just wanted to report this happening, and I'm glad nothing really bad became of it.
Was she maybe asleep, or nodding off? They try to "teleport home," and ... well, maybe if you didn't have your brother's group tag on at the time, she tried to teleport to her "other home." I've been told (don't remember where or by whom, maybe at Kitten's Q&A? ) to "set home" for a kitty taken to another sim, so that it won't do that.
I've seen them jump across sim boundaries ... in different circumstances. I fell off a ramp on my megapuss, once (at a friend's sim), and landed in water on some stranger's parcel, and couldn't ride her through the parcel boundaries ... so I dismounted and was all worried when she poufed. It turned out she had "jumped home" to my friend's parcel -- even though she was not asleep.
Most likely, the avatar was near the edge of the sim (region).
There is a 34 meter boundary around each region where you're actually in two at once. This is done to ease boundary crossings and let you see and talk to people even though they're actually over the line.
Sometimes lag sets in, of course. It's possible for your viewer to think you're on the new region, but the old region still thinks you're there, too. If, during this brief period, the cat is dropped, the old region will quite happily take control of the object.
Now, you cat wants to teleport Home, and Home happens to be on that region. It can't do that all at once. It need to move in fits and starts, working its way IN A STRAIGHT LINE from where it is, to where it wants to end up.
Usually, this works fine.
But, say you're up at 4000, at one corner, and Home is at 20 at the other. The cat needs to move nearly 8000 meters .. 100 or so at a time .. slantwise across and down the sim. OK, it can do that.
But, along the way, what happens if it hits a No Entry parcel? It stops! It can't go forward. So it sits, floating somewhere between 4000 where it started, and 20 where wants to end up .. on the line it wanted to travel.
*sigh*
Area Search is your friend.