How do I override upper-case of @href in my keyref document?

I'm setting up a keyref to map href paths for xref linking.  However, SDL converts the @href entry to uppercase.  The output creates a URL that is all upper-case, which renders the link as invalid.

Now I'm forced to adjust my OT plugin to convert the @href to lowercase.  I can understand (slightly) why SDL does this for an @id but why, why does it insist on doing this for a keyref document, which is strictly used for indirection?