Well I don't know of any special trick, I've used them a fair bit in my current life states dynasty and not had any issues, a spare learnt gardening from one which surprised me at the time, this was after I'd finished the challenge, but when I thought back he had gone on a field trip to the science facility so maybe he learned just enough while there to trigger the skill boost.
My challenge sims stayed well away from anything the other was doing apart from that one time with the sprite sharing, after that I didn't use any more skill boosters as I knew she would probably learn advanced tech if I did. It is odd though and if I'd thought there was the possibility that might happen I wouldn't have touched them either.
Like Chare I disabled seasons but I can't see how that made any difference
I just don't know, most of the ones my sims drank seemed to fail to do anything whatsoever so I gained little benefit from them, I'm just glad now I didn't get an unexpected skill after reading this.
