The BOINC client seems to lose WUs every once in a while. I have lost 1 of 2 CP WUs on the machine I use most since I started. The admin interface shows that I had two issued and I saw the client working on both shortly after I signed up. Both WUs show as In Progress with an unknown outcome on the host results screen. One of the WUs did not ever trickle.

I have also seen it lose WUs from SETI. I saw it lose one SETI WU when I quit and restarted. I had two in progress and when I restarted, I had fewer SETI WUs and only one SETI WU in progress. The CP WU that I lost was also in progress.

I am running the 4.05 client on Windows XP SP2