[chryuop]

Yea that is most of the people I asked told me. But if you go on yahoo Japan there is well almost 三万人 that use this expression. If I typed on a search engine a grammatical error in my language (Italian) I might get few tens or maybe a hundred result, probably all typos or a few not speaking well Italian.
But I can't believe 30,000 Japanese speak bad Japanese.
Last time I encountered it if I well remember it was on the NTV's forum (Japanese channel) one of the messages had in it a phrase ending よいでした。
As I said I will never use it, but for someone who doesn't speak any Japanese, hearing so many Japanese people using it and (one of them comes to my dojo so he told me in my face it is correct) gives me doubts.

Might be some dialect or old expression?