In Patch Preview would be better named "Auto Load to Instrument". Because when it is enabled, the selected sound is added to the selected instrument/layer, overwriting whatever existed, with no way to undo other than to navigate back to the original sound. The behavior of this is fine, it is just misleading to label it as a preview and describe it the way it is in the manual. It's taken me 6 months to really grasp what's actually going on with these preview & load options.
Additionally, In Patch Preview (or whatever it's called) should actually update the Target section with the chosen sound, so it is made clear a change has happened. In actuality, this is a bug - nothing happens in this Target area when loading a new sample, period.
It may also make more sense to put the Load button up with Preview or Details because that is the object that is being loaded (the file). It could be made even more clear by naming the button "Load to Target".
Basically, drag & drop to the pads in the Main view is great until you start working with layers and then things start to get a little messy.