Content-length header is updated no matter what

[irsdl]

Here is a request I am trying to send in Stepper but I don't want it to update the CL header:

POST /foo HTTP/1.1
Accept: image/gif, image/jpeg, image/pjpeg, application/x-ms-application, application/xaml+xml, application/x-ms-xbap, */*, text/w42f61mqgg5
Accept-Language: en-GB
Accept-Encoding: gzip, deflate, w42f61mqgg5
Host: b8.ee
Connection: keep-alive
Origin: https://w42f61mqgg5.com
Content-Type: application/x-www-form-urlencoded
Content-Length x: 35

GET /robots.txt HTTP/1.1
X-YzBqv: 

This setting is disabled in config but it's being applied when you view it in Logger:

[C0DEbrained]

Looks like this is caused by the Burp API automatically updating the content-length header when this line is executed:
https://github.com/CoreyD97/Stepper/blob/215169e1b2920bbbf503e34a89d11e31fa3f25f8/src/main/java/com/coreyd97/stepper/MessageProcessor.java#L295

Hopefully the Montoya API doesn't have this problem, but I guess we'll find out when I update this to that API...