Recently sliced up a model that needed supports, and in the preview I found many areas (which I'll coin a "floating feature") that were unsupported, which I found odd. I tried both the manual support and auto support generation and they both gave the same results. So I made up a really simple model that exposes the failure and tried it: Same problem. I have an image that shows the problem below:
Am I missing an obvious setting, or is this a bug?
Here is the test stl with a floating feature:
As a test I sliced this in Makerware, and proper supports were generated:
In the meantime my workaround was just to add in manual supports where I noticed unsupported features. But the real model I'm printing is far more complex than the example, so I have no good way of knowing if I've caught all the floaty-bits or not.