DVD Media Concern, Adhesive bubble in middle

I am concerned about a "air bubble" in the center of several DVD's I have that are part of a collection. They seem to play fine but it seems as though not enough adhesive made it to the center of the hub to completely seal the 2 platters..?

This is a very expensive set so how concerned should I be that they could come apart?

 

if i paid good money for such a set i would be inclined to return or exchange them .