I have an active sieve file for my list account that alters the headers for this
list (sets the reply-to address to the list instead of the poster) which is
suddenly failing.
require [ "regex", "variables", "fileinto",
"envelope", "mailbox", "imap4flags",
"editheader" ];
/* other stuff */
elsif header :contains "List-id" "dovecot.dovecot.org" {
   if header :matches "Reply-to" "*" {
      deleteheader "From";
      addheader "From" "${1}";
      deleteheader "Reply-To";
      addheader "Reply-To" "dovecot at dovecot.org";
      addheader "X-Covisp-Reply-To" "True";
      }
   fileinto :create "dovecot";
stop;} 
And the trace file:
  55: header test
  55:   starting `:contains' match with `i;ascii-casemap' comparator:
  55:   extracting `List-id' headers from message
  55:   matching value `Dovecot Mailing List <dovecot.dovecot.org>'
  55:     with key `dovecot.dovecot.org' => 1
  55:   finishing match with result: matched
  55: jump if result is false
  55:   not jumping
  56: header test
  56:   starting `:matches' match with `i;ascii-casemap' comparator:
  56:   extracting `Reply-to' headers from message
  56:   finishing match with result: not matched
  56: jump if result is false
  56:   jumping to line 63
  63: fileinto action
  63:   store message in mailbox `dovecot'
  64: stop command; end all script execution
      ## Finished executing script '.active_sieve?
Neither the reply-to header nor the x- header are actually getting added, but
the block is getting executed and the mail is filed in the right folder.
In dovecot.conf I (still) have:
managesieve_sieve_capability = editheader fileinto reject envelope
encoded-character vacation subaddress comparator-i;ascii-numeric relational
regex imap4flags copy include variables body enotify environment mailbox date
ihave