When I upload new images into a post, the gallery tab is available.
When inserting images directly from the media library, no gallery tab is available.
Is this expected behavior? Just wanted to make sure a plugin wasn't interfering with the gallery function somehow.
The gallery is relative to the post, that is it's a collection of images which are attached to the post you're currently working on.
So you will only see the gallery tab when launching the media uploader/inserter window from an Edit Post page, and that post has images attached to it.
Thanks, that's what I needed to know. :-D