Bug with duplicate spell? Realm of Magic pack.
I am unsure what causes it. But sometimes you're clones won't expire and will become full sims that are considered siblings. I've done a lot of testing and I can't find a consistent thing to trigger it. One thing that seemed to trigger it was killing my clone with fire then bringing them back to life. But that's not what happened the first time because the first clone to do this never died. I thought maybe if you left the lot when they were supposed to expire they just wouldn't ever but I tested that out and they expired anyways. The one who became permanent does not have any "Command:" options like normal copies do. I've also occasionally seen "You can't command evil clones" and the command thingie is greyed out. At least in this case I don't know if it's consistent but after the time for it to expire, it stayed and the only change was the grayed out command option was now gone. So it may be an intended feature? That is duplicate "fails" it creates an "evil" clone that won't expire. But I am not 100% sure on this. Neither the new, or original surviving clones had the evil trait even though I distinctly remember the new one saying you cannot command an evil clone. They also don't seem to be particularly mean or unfriendly to my sim I just can't command them. If this is intended perhaps make it so it says "Can't command free clone" or something? I'm not really sure. Either way it can be frustrating not knowing what caused it. I spent several real life hours testing things out the other day. I know that I became overcharged about 5 times to see if it was an overcharge effect but every single one of those expired naturally they just seemed to last longer then ones cast at normal charge. I like this spell but I don't want to have like 50 clones running around the neighborhood. Via backsaving I still only have one surviving clone and I've stopped saving while a clone is out just in case. I did invite the one surviving clone to my sims wedding. They're considered siblings but their relationship isn't super high.