From the Wikipedia article, it sounds like the short could be internal or external at the trace/component/solder joint level. Maybe oversize solder globs work fine until they reach a level of thermal expansion that causes the short circuit, turning a four gate implementation into a three gate config . . . or worse? Could you have fixed you initial problem doing re-flow and borked a simple solder joint while you were at it?

Dunno, just a WAG on my part, I do 3-D electron plumbing, not electronics by any stretch of the imagination.