Every now and then, I look at questions with a different view than "Active". When I do, it often doesn't show some questions that showed under "Active", or shows questions that weren't shown then.
For example, just before I wrote this, there was a question on MSO that showed up under the Newest Questions tab, was asked 7 minutes ago, but doesn't show up under the Active Questions tab (although it was asked after most of those were modified). (EDIT: It's now under Active as well, suggesting some sort of caching issue).
On MSU, I've noticed a day-old question that appears under Active, but not on the homepage or under Votes (it's at -19, so that might be why it isn't on the homepage, but why isn't it under Votes?).
Why is this?