TEST: osr_compd_6 ... Expected:
COMPD_CS["UTM Zone 11, Northern Hemisphere + Unnamed Vertical Datum",
    PROJCS["UTM Zone 11, Northern Hemisphere",
        GEOGCS["GRS 1980(IUGG, 1980)",
            DATUM["unknown",
                SPHEROID["GRS80",6378137,298.257222101],
                TOWGS84[0,0,0,0,0,0,0]],
            PRIMEM["Greenwich",0],
            UNIT["degree",0.0174532925199433]],
        PROJECTION["Transverse_Mercator"],
        PARAMETER["latitude_of_origin",0],
        PARAMETER["central_meridian",-117],
        PARAMETER["scale_factor",0.9996],
        PARAMETER["false_easting",500000],
        PARAMETER["false_northing",0],
        UNIT["Meter",1]],
    VERT_CS["Unnamed",
        VERT_DATUM["Unnamed",2005,
            EXTENSION["PROJ4_GRIDS","g2003conus.gtx,g2003alaska.gtx,g2003h01.gtx,g2003p01.gtx"]],
        AXIS["Up",UP],
        UNIT["Foot_US",0.3048006096012192]]]
Got:
COMPD_CS["UTM Zone 11, Northern Hemisphere + Unnamed Vertical Datum",
    PROJCS["UTM Zone 11, Northern Hemisphere",
        GEOGCS["GRS 1980(IUGG, 1980)",
            DATUM["unknown",
                SPHEROID["GRS80",6378137,298.257222101],
                TOWGS84[0,0,0,0,0,0,0]],
            PRIMEM["Greenwich",0],
            UNIT["degree",0.0174532925199433]],
        PROJECTION["Transverse_Mercator"],
        PARAMETER["latitude_of_origin",0],
        PARAMETER["central_meridian",-117],
        PARAMETER["scale_factor",0.9996],
        PARAMETER["false_easting",500000],
        PARAMETER["false_northing",0],
        UNIT["Meter",1]],
    VERT_CS["Unnamed",
        VERT_DATUM["Unnamed",2005,
            EXTENSION["PROJ4_GRIDS","g2003conus.gtx,g2003alaska.gtx,g2003h01.gtx,g2003p01.gtx"]],
        AXIS["Up",UP]]]
fail
    SRS differs from expected.