I'm running 6.10.58 and .60 and if I set Collatz up as the backup it still loads the cache. I haven't migrated to the newer versions of BOINC so they may have fixed the problem.
That may or may not be the client's issue. Like I said, It ALSO requires the BOINC server to be of a certain version. FWIW, 6.10.58/60 do have the feature. And it works fine for me.
"Don't confront me with my failures, I had not forgotten them" - Jackson Browne