This confused me a bit earlier today when trying to create release notes for our next release, I searched for
any(Project1), any(Project2) updated after 2014/03/29
And got almost no results, and none from our last milestone.
I then searched for Project1 updated after the same date and all of the expected tasks showed up.
It seems like a bug that any() does not handle subprojects/milestones while the regular AND search does.