This particular work unit has been returned by other person 2 days ago. And for some reason server managed to sent it out to you. And since server already had results of this unit from before, it dumped yours.
Another, more likely situation is, that you received this WU before that other person received it, but since you did not fold it continually you did not finish it by the set deadline, at that point WU was re issued. You were still folding and finished after the re-issued WU was returned by someone with faster hardware.
muziqaz wrote:...And since server already had results of this unit from before, it dumped yours...
AFAIK, a Server will not dump a WU that it legitimately assigned even if it received the original WU. It was dumped because it either failed the validation check or (and this few weeks ago) a Server configuration was being investigated to see if that could be causing the issue.
ETA:
Now ↞ Very Soon ↔ Soon ↔ Soon-ish ↔ Not Soon ↠ End Of Time
muziqaz wrote:but since you did not fold it continually you did not finish it by the set deadline, at that point WU was re issued. You were still folding and finished after the re-issued WU was returned by someone with faster hardware.
No, I was folding it continually, and with decent hardware too, never paused it and it was definitely way before the timeout.
Can you post the section from the log when it was assigned to you? And also, considering the log does not have the date, maybe indicate the day when you received it?