See the inappropriate normalization here: https://en.wikiquote.org/w/index.php?title=Wikiquote%3AVillage_pump&diff=prev&oldid=3255699
Description
Event Timeline
I do understand the parser confusion, since it was dealing with already-invalid markup -- note that it didn't add a blockquote, it just removed a meaningless closing-blockquote that didn't have a matching opening-blockquote.
It adding the newline and thus splitting the lists seems not-ideal, though.
I don't *think* that parsoid would ever split an existing list in two during selser, so my intuition is that this is probably more likely a DT-side bug w/ the DOM normalization that you are doing.
Removing the stray closing blockquote is something we would do, but generally we wouldn't touch unrelated list items, and certainly not items in a completely separate list.
Scott: I wouldn't be so sure that Parsoid didn't do this ;-) There are edge case in the newline separator insertion code -- and that whole code needs an overhaul some day based on all the accumulated knowledge of the last decade and test cases. But, yes, it could be a result of the HTML we got from DT. Anyway, all I am saying is "Needs investigation".
A combination, maybe? DT's DOM-fiddling removing that invalid </blockquote>, which then made that node get through selser and allowing the newline to get added incorrectly by parsoid.