Wanted to bump this: This hasn't
been fixed in 3.0:
I've had a number of failed prints because of this issue: Imagine a complex model of a bust/head with stuff hanging off it (locks of hair, gizmos, etc): It has lots of these 'floating features': You'd expect the slicer to catch them (based on my time with Makerware / RepG), but it doesn't, so the first print fails: I have to manually identify all the parts with spaghetti spilling out the bottom, and go back in and manually add the support.
3.0 has a ton of great fixes, but I would consider this a fundamental feature that is still missing
Basically, any time I have S3D auto-add support, I then have to go in and manually check everything and add in whats missing.
add this to your fix list.