Thanks a lot for the very clarifying video, Daren. It really seems to be a problem of gapping, but as I have never done it and I’m playing with a borrowed melodica, I think I prefer to take it to someone who already knows how to do it.
I also wanted to share with you that I recently bought my own P37D Yamaha. I’m loving it, it sounds great and it’s a lot bigger than my friend’s brazilian model. I used a lot of information from this forum to make up my mind on which melodica to buy, so thanks a lot everyone! =D