I tested this in my save and I no longer see this issue.
I will mark it as fixed.
One of my Sim children had just maxed the Mental skill, and got a whim to play Arithmetic Attack. While doing so, her Motor skill very quickly went from 0 to 10.
I saw a very similar thing happen with this Sim's mother when she was a child, and her Creative skill went from 0 to 10 while doing something unrelated to that skill on the computer.
I'm on Mac OS 10.10.5 (Yosemite), all expansions and packs, no mods or CC (ever).
Just had this happen with an half alien child playing keyboard commander she was granted level 1 to level 10 rapidly one after another on the computer that comes with the science career. Saw this happen to an alien child once before on a regular computer.
