you are only suppossed to sew over them if they are nylon teeth and then its at the end or when. normally by default the needle will push the plastic part of the zipper to the side so it doesn't go into the teeth. I too have a viking high end machine and have no problem even with the in the hoop projects that does it all; that's how I make my zipper coin purses. Make sure your needle it all the way up, turned the right way, flat side of needle goes a certain way in all machines and make sure its tight.

that seems so hard to do. I have always shortened from the bottom. I have sewn around the ending where I want it to be, by hand, a lot of times around, and then cut it off. Once it is sewn in it has never come apart at the bottom. I'm talking about a metal zipper. Nylon ones are easier.

I agree that, for metal zippers, adjusting the length from the bottom is the way I was taught many moons ago. For nylon, though, just sewing over it seems to be working out just peachy.

I just use the bar tack stitch and set it for the length for the needle to hit on either side of the zipper slide. It never hits the zipper portion. You can use your regular stitch until you get to the zipper then set it for bar tack.

I don't have that problem with my machine, but would suggest that you do a hand tack over the zipper if it bothers you, and if you are putting that little tab on it, just sew to the tacked part and skip over the zipper

I sew up to the teeth, then hand "walk" the needle past the teeth. Needles are too expensive to waste. I am also using coil zippers instead of the ones with actual teeth. My coun purses are easy. Just two pieces of fabric 5 x 7" sew a zipper in between, (open zipper!) put the fabrics face to face, then sew around the three sides. Easy peasy, and you can run with the idea from there!