Without knowing the chemistry, it's hard to be certain. However, pinholes are caused by outgassing of volatile materials. These are caused by low boiling components in the potting/casting compositions, or are generated by the chemistry of these recipes while they are curing.
Some curing reactions will "give off" low boiling by-products, while other chemistry types do not. If I had more information, we could nail it down. Also, with proper equipment this could be absolutely proven (for example trace analysis of the vapors while curing occurs).
More info about the process and materials = MUCH better answer.
Jim Willimas is a PhD Chemist in Polymers and Materials Science. He specialize in printing, cleaning, inks, and coatings used in electronics manufacturng operations. Williams has more than 30 years experience.
Check the solderability of that component. An x-ray at the pin hole location will reveal more (ie how deep is the hole and how big internally).
Managing Director, Asia Pacific
EH Lim has been in the PCB Assy industry since 1985, starting at Thomson/Singapore for 5 years before moving to Electrovert Asia Pacifc. Lim was Sales Director for Vitronics Soltec prior to joining ECD in 2007 as Managing Director for Asia Pacific.