For things that are like primary keys and don't exist in some segments (worst case is primary/unique key that only exists in 1)
we do wasted seeks.
LUCENE-2694 tries to solve some of this issue with TermState, I'm concerned we could every backport that to 3.1 for example.
This is a simpler solution here just to solve this one problem in termquery... we could just revert it in trunk when we resolve
but I don't think we should leave things as they are in 3.x