Yes that's normal. It's just an oddity with the quake 3 engine where it requires you to put synch to 1, turn on record, and put it back to 0. It will continue to record after it is put on 0 and will eliminate the performance hit. I definately wouldn't recommend trying to play with g_synch 1 on
edit: reread your question: it's normal for both games it's just jedi academny is more resource intensive so you probly notice it more when doing it in JA then in JO. There's no reason to play with it on though, just begin recording and turn it back off. Better yet, find a demo script that'll do it for you (quake 3 one's work just fine).