The fix in #22 solved the problem at hand and doing what was expected
from the specified parameters. Unfortunately it also removed the slightly
hacky "feature" that makes the web mercator work in pj_transform. The
web mercator is special since the latitude is computed on the ellipsoid,
but behaves as if if was defined on a sphere. Hence it is problematic to
change the ellipsoid parameters when using the web mercator, even though
that is the geodetically correct thing to do. The web mercator is used in
more or less any web mapping application and is thus one of the most
frequently used transformations in PROJ. This justifies re-introducing
the minor bug reported in #22.
The problem will have to be taken care of properly when pj_transform
is removed from the library in favour of the transformation pipelines
based API.