Mesorah, Mesorah

In our community, there are a handful of Jews of German (Yekke) extraction whose minhag it is to wash before making Kiddush, which nobody else does around here, which makes them feel like misfits.

Our study group decided to look into the origins of this minhag. It is a long involved story which I wont get into here, but the thing that bothered me is the following.

Rabbi Yosef Karo, in Beis Yosef follows the ruling of the Tur, who along with the Rambam and other Sephardic rabbis ruled that Kiddush should be said prior to washing for bread. In his commentary he mentions that he is amazed to find that many Sephardic Jews do not follow this minhag (meaning they wash prior to Kiddush).

Likewise, the Rema in his emendations on the Shulchan Aruch says to the effect of "I am amazed that there are any people that don't wash before Kiddush. In my entire life I have never seen anyone do anything different (than wash before Kiddush). He further states that this should be a custom that should go on unchanged forever. However, the TaZ, who lived just after the Rema, already stated that though the Rema's opinion was valid, if a person chooses to wash after Kiddush, it should not be looked upon as doing something wrong or inferior.

So my point is - here is a minhag that flip flopped generation to generation, even though key Rabbinic figures ruled on it. What makes us think that any of our mesorahs are rigidly preserved going back to Sinai?