When tagging files with certain characters, the tags are shown correctly in the GUI interface, but when they are actually saved to the file, they are not what is shown in the UI, and also are inconsistently handled between fields.

Example:

https://musicbrainz.org/release/4f33dd9f-bbcd-488a-a755-c3678342caf1

The Artist/Album Artist tags (TPE1, TPE2) for these tracks should be "Ēbn-Ōzn", and that is what Picard shows will be saved.  However, when I look at the tags with another viewer, such as kid3, what is actually saved is "?bn-?zn".

What is saved to the TSOP and TSO2 tags is "Ebn-Ozn" (not including the macron diacritic).

This may have to do with the fact that I am using id3v2.3 and ISO-8859-1 encoding (because UTF16 sucks and isn't handled by many devices).  Perhaps ISO-8859-1 can't properly encode these vowels with macron diacritic?  But if that's the case, why isn't it falling back to standard vowels without the diacritic (as is being used in the sortable tags) rather than a much less useful/more confusing "?" character?