I've generated a Geospatial PDF with GDAL 1.11.3 library.
When I open it with Global Mapper v18, it looks upside down and it's not well georeferenced.
I've opened it with QGIS and with Acrobat Reader, and it seems it's ok.
So I don't know if it's a bug, my file is wrong or Geospatial PDF is not supported.
This is my file geomapa.pdf