When trying to configure a new job, adding a new parameter using the drop-down results in a 403 error message being returned:

403 No valid crumb was included in the request

The logs show:

WARNING: Found invalid crumb <CRUMB_ID>, <CRUMB_ID>. Will check remaining parameters for a valid one...
Aug 14, 2015 5:32:06 PM hudson.security.csrf.CrumbFilter doFilter
WARNING: No valid crumb was included in request for /jenkins//$stapler/bound/dd7670cf-db32-481d-b6f3-6fcdfde6e658/render. Returning 403.

Curiously, when examining the request headers, the crumb is actually being duplicated:

Crumb:<CRUMB_ID>, <CRUMB_ID>

Which is what the logs indicate as well, and claims it's invalid.

Steps to replicate:

1. Go to the configuration of a job.
2. Click on a drop-down like "Add Parameter"
3. Choose a param type, and check request in network dev tools

At the same time, this setup is also running into this bug when deleting projects:

https://issues.jenkins-ci.org/browse/JENKINS-18032

Not sure if they are related.