The Minchas Yitzchak quotes two opinions about the above Rashbah –
1) The Teshuvas Remah – this Rashbah only applies to something which is mentioned in the Poskim.
2) The Heshiv Moshe – the Rashbah even applies if there is no other source.
Correction – the Yerushalmi I thought it was referring in the beginning of Brachos refers to the Chachamim. Or at least I think so.