@Chris Blackbourn (chrisbblend) this was never broken with the default settings, so I don't think anything has changed here.

In T85978#1118897, @Philipp Oeser (lichtwerk) wrote:

Please try a fresh build from https://builder.blender.org/download/

There have been a couple of fixes, now I am getting matching results (first is py version, second is C in current master):

Do you see the same results now?

Also, the newer version ( https://github.com/blender/blender/blob/0e1c6a29cbb21476d6913a592fb12e29bf700b43/source/blender/editors/uvedit/uvedit_unwrap_ops.c#L2017 ) removed the very nice comments in the old version ( https://github.com/blender/blender/blob/ad0da42751596a63a1bc4de5135cd43f7c3921bb/release/scripts/startup/bl_operators/uvcalc_smart_project.py ), which I think is a bit of a shame, given how nicely commented the old version was.