Useless cache warning - "This store doesn't meet the requirements for all known definitions. Definitions for which this store is inadequate will be given the original default store instead of the selected store"

I created a memcached instance and got this as a popup...

"This store doesn't meet the requirements for all known definitions. Definitions for which this store is inadequate will be given the original default store instead of the selected store"

What is one supposed to do with this information? It neither tells you which aspects are not working or what to do about it. This is another instance of the woefully inadequate caching documentation. As, for those of us with load-balanced servers at least, getting this right is now mandatory for acceptable performance this really needs addressed with some urgency.