Hello - I tried it myself and it did not reset my WEP key. Is it possible that you changed your WEP key sometime and that's why it did not match the one on the back of your router? Router reset would revert it back to the original key (which should be the one printed on the back of your router).
Also, which router you using (along with the revision # - You will see that information where WEP key is displayed). I will check more on it.