That's an interesting theory. I do remember exiting CAS resetting my sims, but I don't remember it sending them home. (To be fair, I don't remember a specific time where I sent my sims to CAS while my sims were at work, but with the disgusting amount of time I've logged into the game I just assumed it was at least once.) But even if that's the case, it doesn't account for why my sims are sent back when I open a save file, or also, if this is anything like the last time I had it, why they're sent back whenever I go away from the home lot and then return.
If it isn't a glitch (which I feel like it is, because it went back and forth between acting this way), then it's just a crazy oversight or even some kind of nonsensical game mechanic, both of which I would argue are worse.
I think I'll do some testing. See if it's file dependent and I just got unlucky, and if so, if CAS really has always sent you home.