Credit granted for client error and zero work seconds??? Why?

Not a validator error.

The validator ran on the first three results that arrived. One was invalid. The other two results were valid. Credit assigned to canonical result was the smaller of the credits claimed by the two valid results (43). Then, when the fourth result arrived, it was found valid and given the same credit (43) as the previous two valid results.

[Edited one day later]
As has been pointed out, indeed none of the results was 'invalid'. However due to a BOINC client bug, it claimed zero credit. The remainder of what I have written above is correct. The validator did its job correctly.