Problems with the bolts in the 787 programm

To you remember this experiment in school? You use a steel ball and at room temperature you can put it through a hole with a slightly larger diameter. Now use a Bunsen burner, put heat to the steel ball for a moment and now try the same again: The ball doesn’t fit anymore. A similar trick is used in building airplanes. To ensure that the bolts tightly fit in their holes, you freeze so they get a little bit smaller. They easily fit in their holes. When they get to room temperature, they expand and you have a tight fit between the bold and the both plates you want to connect. Well, so far so good. It looks like, they had an interesting problem in the 787 program as reported by Wall Street Journal. The Seattle Post-Intelligencer writes:

They found that metal bolts, called freeze plugs, inside the wings of one of the six test airplanes had slightly damaged the surrounding material, causing delamination, or cracking, the Journal said, citing "internal company documents and a person familiar with the matter."

Hmm … reading about all this problems … i’m sure i’m waiting a few years before i will put a feet in a 787. I thought, Boeing has already used composites parts in other aircrafts … thought they wouldn’t have such basic problems in the 787.