Didn't Slush fixed that problem? Anyway some pool admins are doing upgrade to 0.8.2 that should help with invalid problems. So Slush do it ASAP...
Invalids are bound to happen occassionally whether there are issues or not; The issue was a slow network connection before that caused us to have a much higher than normal invalid rate. That has been solved but we should still expect a few invalids a week or so.