RFC 5321 (the specification for sending email) doesn't specify a way to forward an email without the originating headers, so what you're trying to do, if kaiten email is written properly, probably breaks something, because you're doing something an email program isn't supposed to do.  (If I were writing another email program, I'd trap the error and either just leave the headers there or tell you that the email can't be forwarded if the headers are changed.  In the past, I treated the headers specified in the RFC as read only - the user had no means of editing them.)
Changing email headers is a security risk.  I could send you an email from PayPal's email server (according to the headers - their MX record is available with a single command).  You'd never know it wasn't from them.  Not nice, huh?  (Some headers, like X- headers, can be changed, because they're unspecified in the RFC, so they mean whatever you want them to mean.  But an originating From: header?  If there were a way of detecting that being changed, I'd set a filter to immediately delete any email like that.)