I would like to share an experience I just had with this issue. I purchased two pairs of ballet flats, one lambskin, one metallic calfskin from a Chanel boutique. The nice SA gave me a bag containing a soft cloth, one small bottle of leather conditioner/cleaner, and one small bottle of stain/water repellent. I applied the repellent to both pairs of shoes. After 24 hours, the lambskin looked perfect. The calfskin had a few white spots of residue. Fortunately, the spots wiped off after some moderate rubbing with the soft cloth. I had been worried, but fought the urge to panic. I honestly think that I did not hold the product far enough away when I was spraying, and that's what resulted in the spots.
Anyways, just wanted to share. I hope all of you are having a fine weekend.