For the sculpting thing, the shadow clone is just how the game makes the ice sculpture so that's not an issue just so everyone knows. That's normal.
Try the save again - I get that error and reload the game just fine afterwards some days. Got it a lot in the end of my dynasty. I need more info on the sculpting thing too. What gets buggy exactly? The exact happenings for you.
I did know that about the shadow clone. I'd always wondered if it was glitched, but I guess not.
As for the glitch, my sculptor sim (either my founder or the other sculpting slave, it does the same for both) asks another sim to model for them, and the model wanders over and poses, just like they're supposed to. Then the shadow clone thing starts, except it never finishes its round (it's supposed to do a big circle around the model, but it stops about halfway, acting like it's finished--in the case of my toddler heir, the shadow sits down and sways back and forth, rather than being frozen mid-crawl like I'd expect), and instead of the ice block appearing like it should, both sculptor and model sit there forever, doing nothing. They move and sway and whatnot, but they're just...sitting there. After a while (like, thirty minutes to an hour in Sims time) I get frustrated and cancel the action, but it continues to stay x-ed out in the queue, and both parties are unresponsive. I can queue other actions, but they won't do anything but continue to sit there while needs bars drop and whatnot. Eventually I do ResetSim on them both (resetting the model snaps them both out of it, but resetting the sculptor only leaves the model still stranded) and they can do other things, but if I try sculpting an ice sim again I get the same glitch, no matter who I use as sculptor or model.
Sometimes, like when I was queuing up my founder for her sculptures, there would be two versions of the model selectable in the popup menu -- one would be my founder with the relationship bars where they are in the game, which I assume is the real one, and one would be my founder as a stranger, which I assume is the clone. One time my founder got a wish to sculpt the paparazzi, so I let her, and the paparazzi ran away (as they often do) with my founder still waiting at the sculpting station, so I canceled the action. Then I saw the paparazzi came back, so when I queued it up again and saw two of the paparazzi listed I selected the one marked "acquaintance" rather than "stranger", which worked fine until right before the paparazzi started modeling and her clone wandered up and started chatting with the original.
So, yeah. If there's a fix, I'd love to know it.