XMP Toolkit SDK - cannot write GPano into jpeg file

Hello,

I'm using XMP Toolkit SDK on iOS, I would like to add GPano metadata to my fresh created jpeg (jpeg is created from scratch with QImage API).

I started from SDK code in "samples/source/ModifyingXMP.cpp", I just added this few lines :

// register namespace
string actualPrefix;
SXMPMeta::RegisterNamespace( "http://ns.google.com/photos/1.0/panorama/", "GPano:", &actualPrefix );

// write GPano metadata
meta.SetProperty("http://ns.google.com/photos/1.0/panorama/", "ProjectionType", "equirectangular", 0);

I use this lines to dump meta content :

SXMPIterator iter( meta );
string schemaNS,propPath,propVal;
while( iter.Next( &schemaNS, &propPath, &propVal )){
    cout << schemaNS << " " << propPath << " = " << propVal << endl;
}

When I dump meta, I have this :

http://purl.org/dc/elements/1.1/  = 
http://purl.org/dc/elements/1.1/ dc:creator = 
http://purl.org/dc/elements/1.1/ dc:creator[1] = Author Name
http://purl.org/dc/elements/1.1/ dc:creator[2] = Another Author Name
http://purl.org/dc/elements/1.1/ dc:title = 
http://purl.org/dc/elements/1.1/ dc:title[1] = An English title
http://purl.org/dc/elements/1.1/ dc:title[1]/?xml:lang = x-default
http://purl.org/dc/elements/1.1/ dc:title[2] = An English title
http://purl.org/dc/elements/1.1/ dc:title[2]/?xml:lang = en-US
http://purl.org/dc/elements/1.1/ dc:title[3] = Un titre Francais
http://purl.org/dc/elements/1.1/ dc:title[3]/?xml:lang = fr-FR
http://ns.google.com/photos/1.0/panorama/  = 
http://ns.google.com/photos/1.0/panorama/ GPano:ProjectionType = equirectangular

So it is ok I see the GPano property when I dump the meta.

But my problem is that I don't retrieve GPano metadata in exported file while I see correctly other XMP properties added by the sample code. I use ApolloOne app or thexifer website to check file metadata.

It looks like GPano property is not exported to file, is it a bug or my misunderstanding?