Some people are still running an older version of the client which only supports resolution to 1 bitcent. You don't lose the the confirmed reward, you just have to accumulate at least .01BTC to get payed out.
I know I didn't lose it as it still shows in my confirmed rewards, but if I can't get it payed out to my client, it's effectively "lost" isn't it? Sure I can accumulate at least .01BTC again, but then anything above and beyond .01BTC (unless you magically hit right at .01BTC) is again effectively "lost".
It's a moot point though, as eleuthria has stated that BTCGuild will support full precision payouts here very soon.