I am not sure that I can add much to this thread.. so why am I posting? Probably an inflated sense of the value of my opinion
I think that I have UI, even if I am in ACBLand (where I am most of the time). As has been pointed out, few players always ask. For myself, I almost always ask about opps' carding and leads when I am declarer and the lead has been made: but almost is not always. If I see no play problem (and in my contracts, there usually is a play problem, but that is another story), i often don't bother.
The same mindset comes in here, even if partner is a frequent asker.
This whole situation is a mess. If you always ask, then you slow down the game and risk offending people. If you seldom ask: you ask only when you think you might bid, then you definitely give UI every time you learn something that causes you to pass instead of bidding.
Here, I think that passing is a LA: you are red, and -100 against their +90 is awful: and of course -200 is the kiss of death. Had partner passed with no expression of interest (or disinterest) would 8 out of 10 players of good quality reopen? I wouldn't, altho I would really want to.
BTW, I think that this was a fair way to post. Roland certainly knows how to post when he wishes to test, through postings, whether an action was or was not a LA in the absence of hestitation. That allows second-guessing of the committee. The way this is posted tests us as if we were the committee: after all, the committee rules when possessed of all the information.
Which is why committees have such a difficult time of it. In order to determine whether UI influenced the result they have to 'disabuse their minds' of the UI and determine what would have happened. Few humans are capable of such mental gymnastics, and thus we get a lot of what is called in NA 'monday morning quarterbacking'.
So keep up the good work, Roland: maybe fending off criticisms of your postings will detract you from the almighty struggle for control of Hans 0
'one of the great markers of the advance of human kindness is the howls you will hear from the Men of God' Johann Hari