Roman Number builtin .v only works on uppercase letters

[kcruijss]

The .v builtin to converts valid Roman Number letters (e.g. I or VC) to integers, but only works on uppercase letters.
I can understand that the reverse builtin .X always converts to uppercase, but just like the builtins for Hexadecimal conversion H and h , I would expect .v/H to work on both upper- and lowercase characters; and .X/h only convert to uppercase.

Try it online to reproduce.
Came across it in this codegolf answer of mine.