Okay, I figured out why I'm seeing different results (or was). Its because my output text layer was below the line layer I was tagging. Its lame, but that's your best bet in 8.3 -- make sure your output text layer when tagging is below the layer you're tagging (and then move it back afterwards). I know, that's not a great solutions, but its all there is in 8.3 I'm afraid.
I took a look at what Illustrator provides in hit testing and unfortunately it's fairly limited. I thought they gave us a list of everything that was hit, but they don't. They just
provide the top-most item that satisfies the hit criteria. Unfortunately, the criteria doesn't have an option to ignore text paths (perversely, there is
an option to ignore everything but
The only ray of hope I can offer is that I have an idea for 8.4 -- it is
possible to limit the hit test to a branch of the art tree. So in 8.4 I'll add a preference to let you limit the Tagger tool to only the current layer. If that's enabled, it will ignore hits on any other layer (well, it will include sub-layers but they're by definition below the current layer) and should make tagging line layers much less painful when 'follow line' is turned out. Of course, it will likely also have an option to 'clip' line-clinging labels to the bare minimum portion of the path so there will probably be two ways to avoid this headache in 8.4!
I'm sorry I can't get it into 8.3.3 (coming shortly) but it didn't feel like a good idea to change the behaviour of the Tagger tool in a minor release -- we'd probably hear from people wondering why we 'broke' the Tagger tool