I doubt that a mapping will save this field.
See this thread about special XML data stored by WIndows for mp4 files:
The Media created field is also part of it.
Currently, there is no way to access that data in MP3tag.
I would like to point out that apparently Windows does not support that in flac files and that MP3tag preserves it in MP4 files.
As I do not have an wma file, it would be a good service by others to test whether this file format is a special case.