Did you use underglaze or glaze? I have had that happen with both.
More likely with underglaze, and not until the final clear coat is fired
on. It's a problem of glaze fit. The clay body might also have so much
talc in it (are you using a low fire white clay?) that certain glazes
won't stick to it. It makes me want to SCA-REEM when that happens. I
used to use a lot of underglazes on my own pieces. I would put 20 hours
of glazingce sometimes, only to have the underglaze shiver off the rim
of a vessel on the final clear coat firing. No way to fix it, either.
It's a problem with the clay shrinking more than the clay as it cools.
ALso, make sure you are firing your bisque to 04...that can make a
difference. My condolences to you.