st_curvetoline not working when casting from geography type

[bcrosby]

The following returns a polygon instead of a curvedpolygon:

select st_astext(st_linetocurve(st_buffer('POINT(-78.8994666666666667 43.9228166666666667)'::geography,5000)::geometry));

However, the following returns valid curved geometry:

select st_astext(st_linetocurve(st_buffer('POINT(-78.8994666666666667 43.9228166666666667)'::geometry,5000)));

[pramsey]

Buffer(geography) returns a true circular buffer on the sphere. When you convert it into geography it's actually oblate, squished, and the there is no arc for the routine to find.