Game caches are used when you want to make a campaign and you want to transfer units and stuff from one map to another.
I suggest you open up blizzard's campaign maps to see what they are doing with the game caches, you will not find any better example of them being used.
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.