[Proj] ESRI's standard_parallel_1 for Mercator morphed to latitude_of_origin?

[Mikael Rittri]

This question really concerns GDAL/OGR rather than Proj.4, but anyway:

I have had a problem that I think was caused by 

http://trac.osgeo.org/gdal/changeset/7542

which caused the Mercator parameter "standard_parallel_1" in ESRI WKT to be
renamed to "latitude_of_origin" during conversion to OGC WKT. 

This makes no sense to me. These are different parameters with different semantics, and according to 
http://www.remotesensing.org/geotiff/proj_list/mercator_2sp.html
both of them are valid parameter names for Mercator (2SP) in OGC WKT.

So why the renaming? Is the semantics subtly different in the ESRI world? 
Or is this just a bug that has survived because a Mercator seldom has a non-zero standard parallel?

I'd be grateful for comments. 

Mikael Rittri
Carmenta
Sweden
http://www.carmenta.com