If you send an Accept header that doesn't contain a slash (i.e., /), CXF's JAX-RS implementation returns a HTTP status of 500 (Internal Server Error). Instead of this status, it would be preferred if a HTTP status of 406 (Not Acceptable) is returned.
Here's the test header:
Here's the current response:
Status Code: 500 org.apache.cxf.interceptor.Fault: Media type separator is missing
Here's the preferred response:
Status Code: 406 Not Acceptable
I've attached a potential patch against trunk for this issue: