Sieve vacation :addresses match only case-sensitive?

The recipients in the vacation :addresses String list are matched case-sensitive.

If the recipient gets a mail with wrong case, the message is discarded with: "discarding vacation response for implicitly delivered message; no known (envelope) recipient address found in message headers"

I think the matching should be case-insensitive.

Is this a bug or do I miss some option?

I'm using Dovecot 2.3.7.2, Pigeonhole version 0.5.7.2.

-- Philipp Fäustlin