I live in southern Ireland, I was educated in a Dublin Grammar school, I was then a student of English in Trinity College Dublin (late 80s). Since I was a nipper its always been "I was sitting there" and "I was standing" He was sitting over there . . . . I was sitting over there too, we were standing, they were sitting, we were all sitting over there!
Then in about 1990 when I was teaching in Surrey, I first heard "I was stood over there" from an other primary school teacher of all people! and from that day onwards I have got more and more dumbfounded as to how this appalling trend has gainded ground in thew South of England, possibly through the mediums of TV & Radio?
Not a day goes by now without some highly paid presenter and/or guest on the BBC, ITV, or Sky uttering the awful grammar "I was sat in the front row" or, they were stood at the bus stop, or we were all sat there, they were all sat over there, etc etc etc . . . . .
Oh, it makes my blood boil.
Interestingly, the traditional/standard forms "I was sitting" and "I was standing" are still the norm in Ireland both North & South, and I have yet to hear the new forn of non-standard 'test speak' grammar in Ireland - Thank God.
I guess the teaching of standard English grammar in English schools has sadly been relaxed, for at least a couple of decades . . .