One of the weird behaviors so far with comment collapsing was that if a
top-level comment was collapsed due to being tagged as "noise", and then
all other top-level comments were also collapsed due to being made up
entirely of old comments, the end result would be all comments being
uncollapsed, including the "noise" one.
This probably still isn't a proper fix for it, but should be better. The
whole system of interactions between different collapsing processes
probably needs re-thinking or this is going to get very confusing as
more "reasons for collapsing" come in.