As Alex pointed out, I neglected to commit move_messages when I modified the copy/move functions.

Thanks Alex!

src/move_messages.php

@@ -209,7 +209,7 @@ if(isset($expungeButton)) {
 } else {    // Move messages
 
     if (count($id)) {
-        sqimap_msgs_list_copy($imapConnection,$id,$targetMailbox);
+        sqimap_msgs_list_move($imapConnection,$id,$targetMailbox);
         if ($auto_expunge) {
             $cnt = sqimap_mailbox_expunge($imapConnection, $mailbox, true);
         } else {