After the replacement of auto smooth with a modifier, sharp edges are
always used, so the "shade smooth", "shade flat", and "smooth by angle"
operators cleared the attribute. However, often users spend significant
time manually tagging edges sharp, and the operators make it too easy to
lose that data.
To keep the old behavior by default, add an option called "Keep Sharp
Edges". Though this can make the operators "ineffective" at their goal
of changing the way the meshes look, or result in redundant data stored
on the mesh, it's a much safer default, especially as users get used to
the new workflow.
Hans Goudey