Plus one on the full mag plus one in the chamber potential for failures. Front Sight, the NV based firearms training institute advises that with Glocks, load 1round short of a full mag, to preclude problems. It's worked to perfection with my wife's G19, Gen 4, over 2000 rounds now with 99.99% reliability...failures (2) were due to my faulty reloads.
If it really bugs you, shootiung with less than a full mag., call Glock...but rest assured that if you didn't get the job done with the first 14 rounds, the 15th probably won't help either.
Best Regards, Rod
Our Flag does not fly because the wind blows against it,
It proudly waves because a soldier's dying breath blows upon it.
USAF Forward Air Controller, 5th Spl Forces,
An Loc, lll Corps, RVN, 69-70, Vietnam Vet '69-'73