For idv3 TXXX frames, Picard is case-sensitive.
That can pose problems for preserving tags from being cleared.
When you have added a tag name to be preserved, and you are not aware another application has written the TXXX frame in capitals, the tag will not be preserved but deleted.
Of course a user could add variations of casing in the preserve field (like keywords, KEYWORDS, Keywords), but that's rather cumbersome, and more importantly, damage may already have been done before the user is aware of this issue in the first place.
Therefore I believe it might be a good idea to make Picard case-agnostic in this regard.