My veneer specialist does not think the problem lies with the glue. He said that veneer does not expand, and that appears to be what has occurred relative to the MDF cabinet. He thinks it is a problem with the MDF substrate. I blame the glue, like Rja believes. [Rja, my edges have completely separated as well.] Upon receipt of the speakers when they were new, I noticed that the veneer had some water damage on some surfaces, so moisture may be a culprit at some level. It also may be a bad run of speakers that were affected. As I said before, my first pair of Dunlavy's were fine (SC-IV's). I have seen a pair of V's with the same veneer release problem that were owned by an investor group member for DAL in 1998-1999.
I discovered a website that discussed matters concerning veneer on MDF substrates. Moisture can be a problem, as well as the glue. Apparently, the best glue bond between MDF and veneer is obtained through applying two coats of glue to the MDF substrate. The first glue coating sort of seals the MDF substrate, while the second glue coating serves as the bonding agent with the veneer. I don't know the veracity of these statements, but it seems to make some sense given the nature of MDF material.
If one applies only one glue coating, then the glue can seep into the MDF material, resulting in less glue being available at the MDF-veneer interface for bonding. If an additional glue coating can provide an adequate seal for the MDF surface, then perhaps that coating prevents changes in the moisture content of the MDF material.
Anyway, I am having a local Chicago veneer shop put fresh veneer skin on my SC-IVa's next week.