4. In foobar no other Vorbis Comments are translated/remapped to a different field name
You are not entirely right.
static const struct {
const char * m_fb2k;
const char * m_vorbis;
} g_remap_table[] = {
{"PUBLISHER","ORGANIZATION"},
{"ALBUM ARTIST", "ALBUMARTIST"},
{"TOTALTRACKS", "TRACKTOTAL"},
{"TOTALDISCS", "DISCTOTAL"},
{"CONTENT GROUP", "GROUPING"},
};
These are the fields currently remapped between fb2k (former) and Vorbis Comments (latter). At some point of time foobar2000 did pass unchanged metadata to Vorbis Comments, but that was a long, long time ago. The CONTENT GROUP part is the only recent addition here.
I suppose the remapping for Vorbis Comments (also affects FLAC/Opus/etc) can cause more annoyance than benefit for some, However, there is a switch in advanced preferences (under Tagging) to suppress the remappings beyond the PUBLISHER/ORGANIZATION line, then you get (nearly) untouched passthrough. Only the switch needs renaming to mention CONTENT GROUP / GROUPING, which I am going to fix now.