I've experienced those same (intermittent) stalling problems with CCC, Retrospect, SilverKeeper, and Tri-BACKUP. I now use SuperDuper, and have had no problems whatsoever.
I'm still a big fan of CCC, and recommend it, yet I have no idea what causes those stalling problems. Thankfully, SuperDuper has lived up to it's name. Also, I should mention that I can't recall DejaVu stalling while doing back-ups.
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