Recording midi in Logic Pro on aux tracks

Since today, I can't record any midi anymore on my aux tracks of my multi instruments. I can still record midi on the first track (the instrument track), but when I start recording the other tracks (on aux tracks), I see the recordings appear, I hear the sounds allright, but when I stop recording, the region that was created just disappears again and there's no recording. I didn't change any settings, and I don't know what is causing this.

Thanks!

Johan