I don't know if this has been brought up, but I will continue with this post.
I have been working on a perl script which will create a ticket in RT using REST. I started using RT::Client::REST 0.31. One of the requirements was the ability populate custom fields on ticket creation. Also needed the ticket to contain all the information it needed from a form on ticket creation. I used RT::Client::REST->create subroutine to create the ticket which was great as I could populate all fields on creation, except for custom fields.
Why was this happening? Well, in REST.pm, it takes all the values provided in the hash in the create subroutine and makes them all lowercase. Custom fields need to start with "CF-" and in that case for them to work.
Line 271, just after the line