Changing MP4::Tag ItemListMap

[Новичков А.А.]

> Take a look at the MP4::Tag source code. The usual way is something >
> like:
> 
> file->tag()->itemListMap()["aART"] = TagLib::StringList("Album artist");
> file->tag()->itemListMap()["\251wrt"] = TagLib::StringList("Composer");
> 
> Or, if you want to write a new free-form tag:
> 
> file->tag()->itemListMap()["----:com.apple.iTunes:foo"] =
> TagLib::StringList("Some custom tag");

I tried 
map.insert("some key",TagLib::MP4::Item(TagLib::StringList("value")));
but nothing happened. 

Is it possible to modify MP4::Tag itemListMap taken by reference?
And what does  the save() method in the MP4::Tag public methods do?

Another problem: when trying to save tags in MP4 file with TagLib extras v.0.1.? (in Ubuntu Jaunty) 
my program crashes with segfault even if I do just
TagLib::MP4::File *f=new TagLib::MP4::File(filename);
f->save();