I had a problem slicing a model where the bottom layer was 'infill' rather than a base.. But after flipping it over a few times and slicking it was fine.
But whilst investigating this, I wasted a ton of time, as the Layer view showed the "skirt" at 0.6mm (3 layers in the air).
When I sliced it without supports, the skirt was at layer 1.. But when I enable support, it goes to layer 3.
BUT.. When I look at the Preview view (And an external GCode viewer), the skirt is on layer 1. So I wonder if this is just a bug in the layer view?
before I report it as a bug, could someone who is more familiar with this verify my findings?