Trying to age up a toddler using a birthday cake, the animation of them blowing out the candles works but as soon as the adult tries to put the toddler sim down, it glitches and resets them, making their arms go up in a weird way and not going through with the aging up trait screen. It ends up breaking the cake, and after multiple tests, with and without mods (MCCC and UI Cheats) I can not age up my sim. I'm playing on short-lifespan if that makes any difference and on a Windows PC.
Edit By crinrict: Adjusted Title to fit old bug report.