This problem was suffered by a potter moving from Europe to Canada. In Europe she used lead based glazes and got smooth defect-free surfaces. But in Canada she began using our Gerstley Borate based glazes and had many problems adapting to them. By using glaze chemistry to both adjust recipes to source boron from frits instead or GB and to reduce their melt fluidity, by bisque firing higher, glaze firing higher, using a finer particle sized terra cotta body and using a drop-and-hold firing schedule (like C03DRH) she was able to eliminate the issues.
Pinholing is a common surface defect that occurs with ceramic glazes. The problem emerges from the kiln and can occur erratically in production.